PolyMet Reports Completion of Drafting of Prelimin

ST. PAUL, MINNESOTA--(Marketwired - May 13, 2013) - PolyMet Mining Corp. (TSX:POM)(NYSE MKT:PLM) ("PolyMet" or the "Company") has been notified by the Minnesota Department of Natural Resources ("MDNR") that ERM, the independent EIS Contractor, has completed drafting the preliminary supplemental draft Environmental Impact Statement ("EIS") analyzing PolyMet's 100%-owned copper-nickel-precious metals NorthMet project located in the established mining district of the Mesabi Iron Range in northeastern Minnesota.

The NorthMet preliminary supplemental draft EIS will be reviewed by the Co-Lead Agencies (MDNR, the US Army Corps of Engineers, and the US Forest Service) and the Cooperating Agencies (the U.S. Environmental Protection Agency and the Bois Forte, Fond du Lac, and Grand Portage Tribal Governments) prior to publication of the supplemental draft EIS for public review later this summer.

"This is a very important step toward completion of the environmental review and issuance of the permits we need to build and operate the NorthMet Project," stated Jon Cherry, President and CEO of PolyMet. "The Agencies and their EIS Contractor have been engaged in very detailed review of the project design, which includes several project modifications in response to public and regulatory comments. The project modifications and improvements, such as the addition of a Reverse Osmosis water treatment plant, demonstrate our commitment to construct and operate NorthMet in a way that protects the environment."

About PolyMet

PolyMet Mining Corp. ( www.polymetmining.com ) is a publicly-traded mine development company that owns 100% of Poly Met Mining, Inc., a Minnesota corporation that controls 100% of the NorthMet copper-nickel-precious metals ore body through a long-term lease and owns 100% of the Erie Plant, a large processing facility located approximately six miles from the ore body in the established mining district of the Mesabi Range in northeastern Minnesota. Poly Met Mining, Inc. has completed its Definitive Feasibility Study and is seeking environmental and operating permits to enable it to commence production. The NorthMet project is expected to require approximately two million hours of construction labor, creating approximately 360 long-term jobs, a level of activity that will have a significant multiplier effect in the local economy.

POLYMET MINING CORP.

Jon Cherry, CEO

This news release contains certain forward-looking statements concerning anticipated developments in PolyMet's operations in the future. Forward-looking statements are frequently, but not always, identified by words such as "expects", "anticipates", "believes", "intends", "estimates", "potential", "possible", "projects", "plans", and similar expressions, or statements that events, conditions or results "will", "may", "could", or "should" occur or be achieved or their negatives or other comparable words. These forward-looking statements may include statements regarding our beliefs related to the ability to receive environmental and operating permits, job creation, or other statements that are not a statement of fact. Forward-looking statements address future events and conditions and therefore involve inherent known and unknown risks and uncertainties. Actual results may differ materially from those in the forward-looking statements due to risks facing PolyMet or due to actual facts differing from the assumptions underlying its predictions.

PolyMet's forward-looking statements are based on the beliefs, expectations and opinions of management on the date the statements are made, and PolyMet does not assume any obligation to update forward-looking statements if circumstances or management's beliefs, expectations and opinions should change.

Specific reference is made to PolyMet's most recent Annual Report on Form 20-F for the fiscal year ended January 31, 2013 and in our other filings with Canadian securities authorities and the U.S. Securities and Exchange Commission for a discussion of some of the risk factors and other considerations underlying forward-looking statements.

PolyMet has filed a registration statement (including a prospectus) with the U.S. Securities and Exchange Commission, for the offering to which this communication relates. Before investing, prospective investors should read the prospectus in that registration statement and other documents the issuer has filed with the U.S. Securities and Exchange Commission, for more complete information about PolyMet and this offering. The documents are available free of charge by visiting EDGAR on the U.S. Securities and Exchange Commission website at www.sec.gov . Alternatively, PolyMet will arrange to send you the prospectus if you request it by calling 1 - 416 915-4149 .