"In order to ensure a fair and transparent auction, we came to a conclusion that POSCO is not eligible for the bid," the state-run bank said in a statement.
The decision came after POSCO's consortium partner, GS Group, suddenly pulled out of the deal to jointly bid for a controlling stake in the world's third-largest shipbuilder.
KDB is a top shareholder of the shipbuilder and is advising itself on the deal.
Hyundai Heavy Industries (009540.KS: Quote, Profile, Research, Stock Buzz), the world's biggest shipbuilder, and chemical and energy-focused Hanwha Group also submitted final bids separately.