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EXHIBIT 12.1

CERTIFICATION

I, Joseph Scipioni, certify that:

|1. | 1. I have reviewed this annual report on Form 20-F of
        PolyMet Mining Corp., as
        amended by this Amendment No. 1 on Form 20-F/A;                                                                                                                                                                                                       
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|2. | Based on my knowledge, this report does not contain any
      untrue statement of a material fact or omit to state a material fact
      necessary to make the statements made, in light of the circumstances under
      which such statements were made, not misleading with respect to the period
      covered by this report;                   
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|3. | Based on my knowledge, the financial statements, and
      other financial information included in this report, fairly present in all
      material respects the financial condition, results of operations and cash
      flows of the company as of, and for, the periods presented in this
      report;                                         
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|4. | The companys other certifying officer and I are
      responsible for establishing and maintaining disclosure controls and
      procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and
      internal control over financial reporting (as defined in Exchange Act
      Rules 13a-15(f) and 15d-15(f) for the company and
have:

(a) Designed such disclosure controls and procedures, or caused
  such disclosure controls and procedures to be designed under our supervision,
  to ensure that material information relating to the company, including its consolidated
  subsidiaries, is made known to us by others within those entities, particularly
  during the period in which this report is being prepared;

(b) Designed such internal controls over financial reporting,
  or caused such internal control over financial reporting to be designed under
  our supervision, to provide reasonable assurance regarding the reliability of
  financial reporting and the preparation of financial statements for external
  purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the companys disclosure
  controls and procedures and presented in this report our conclusions about the
  effectiveness of the disclosure controls and procedures, as of the end of the
  period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the companys
  internal control over financial reporting that occurred during the period covered
  by the annual report that has materially affected, or is reasonably likely to
  materially affect, the companys internal control over financial reporting.

|5. | The companys other certifying officer and I have
      disclosed, based on our most recent evaluation of internal control over
      financial reporting, to the companys auditors and the audit committee of
      the companys board of directors (or persons performing the equivalent
      functions):
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(a) all significant deficiencies and material weaknesses in the
  design or operation of internal control over financial reporting which are reasonably
  likely to adversely affect the companys ability to record, process, summarize
  and report financial information; and

(b) any fraud, whether or not material, that involves management
  or other employees who have a significant role in the companys internal
  control over financial reporting.

|Date: May
      27, 2011 | /s/
      Joseph Scipioni                                
|------------------------ | ---------------------------------------------------------
|                         | Name: Joseph Scipioni                                    
|                         | Title: Chief Executive Officer (Principal
      Executive
|                         | Officer)                                                 



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