C3is (CISS) F-1/ARegistration statement (foreign) (amended)

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the use in this Registration Statement No. 333- 271228 on Form F-1 of our report dated April 12, 2023, relating to the combined financial statements of C3is Inc. Predecessor. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/ Deloitte Certified Public Accountants S.A.

Athens, Greece

June 6, 2023