The Diet cleared a free-trade agreement with Malaysia on Wednesday, bringing the pact one step closer to coming into force by summer.
To complete the ratification process, the Diet still needs to pass related bills concerning rules on product origin and tariff rates, officials said.
In Malaysia, ratification does not require legislative measures, only administrative procedures.
The FTA was signed in December after nearly two years of negotiations. Malaysia will be Japan's third FTA partner, following Singapore and Mexico.
The two nations will remove tariffs on essentially all industrial goods and most agricultural, forestry and fishery products within 10 years.
Talks with Vietnam
Japan and Vietnam began their second study session in a three-day run Wednesday to explore the possibility of signing a bilateral free-trade agreement.
During this meeting in Tokyo, Japan aims to conclude a feasibility study on launching formal FTA talks later this year, an official said.
The study sessions began under an agreement between Prime Minister Junichiro Koizumi and his Vietnamese counterpart, Phan Van Khai, in December.
Vietnam is a member of the Association of Southeast Asian Nations, which strives to conclude FTA talks with Japan by next March.
Among ASEAN, Japan has an FTA with Singapore and has signed one with Malaysia. It has struck basic accords for similar undertakings with the Philippines and Thailand and is in official talks with Indonesia.
The other ASEAN economies are Brunei, Cambodia, Laos and Myanmar.