<page>								EXHIBIT 31.02
CERTIFICATIONS

I, Kevin Perry, Chief Financial Officer of Demeter Management
Corporation (?Demeter?), the general partner of the registrant, Dean
Witter Cornerstone Fund III, certify that:

1.	I have reviewed this quarterly report on Form 10-Q of the
registrant;

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.

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 registrant as of, and for, the
periods presented in this report;

4.	The registrant?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
registrant 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 registrant, 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 control 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 registrant?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
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          d)	Disclosed in this report any change in the registrant?s
internal control over financial reporting that occurred
during the registrant?s most recent fiscal quarter (the
registrant?s fourth fiscal quarter in the case of an
annual report) that has materially affected, or is
reasonably likely to materially affect, the registrant?s
internal control over financial reporting; and

5.	The registrant?s other certifying officer and I have
disclosed, based on our most recent evaluation of internal
control over financial reporting, to the registrant?s
auditors and the audit committee of Demeter?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 registrant?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 registrant?s internal control over financial
reporting.









Date:   August 15, 2005        /s/	Kevin Perry
		Kevin Perry
		Chief Financial Officer,
		Demeter Management Corporation,
                             		general partner of the registrant