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EXHIBIT 12.2

CERTIFICATION

I, Douglas Newby, certify that:

I have reviewed this annual report on Form 20-F of PolyMet
Mining Corp.;

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;

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;

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.

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):

(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: April 30, 2009 | /s/
      Douglas Newby                                  
|-------------------- | ---------------------------------------------------------
|                     | Name: Douglas Newby                                      
|                     | Title: Chief Financial Officer (Principal
      Financial
|                     | Officer)                                                 

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