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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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FORM 6-K

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REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16
UNDER THE SECURITIES EXCHANGE ACT OF 1934

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For the month of August 2026

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Commission File Number: 001-41858

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Okeanis Eco Tankers Corp.

(Translation of registrant’s name into English)

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c/o OET Chartering Inc., Ethnarchou Makariou Ave., & 2 D. Falireos St., 185 47 N. Faliro, Greece

(Address of principal executive office)

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Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

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INFORMATION CONTAINED IN THIS REPORT ON FORM 6-K

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Attached to this report on Form 6-K as Exhibit 99.1 is a copy of the press release published by Okeanis Eco Tankers Corp. (the “Company”) on August 4, 2026, titled “Okeanis Eco Tankers Corp. - Unaudited Condensed Financial Statements for the Second Quarter and Six-Month Period of 2026.”

Attached to this report on Form 6-K as Exhibit 99.2 is a copy of Management’s Discussion and Analysis of Financial Condition and Results of Operations and the Unaudited Interim Condensed Consolidated Financial Statements of the Company for the Six Months Ended June 30, 2026.

This Report and the exhibit(s) hereto are hereby incorporated by reference into the registrant’s registration statements: (A) on Form F-3 (File No. 333-287032), filed with the Securities and Exchange Commission on May 7, 2025 and declared effective on May 21, 2025 and (B) on Form F-3 (File No. 333-287036), filed with the Securities and Exchange Commission on May 7, 2025 and declared effective on May 21, 2025.

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SIGNATURE

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Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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