Simmons & Simmons plans to open a branch in Tokyo, having successfully pulled together its Shanghai and Hong Kong offices into an integrated China practice earlier this year.
Huen Wong, managing partner of the new China practice, said the firm was looking to build a regional presence with the Tokyo base and another South East Asian office.
He said: "Pooling together the Hong Kong and Shanghai offices has allowed us to better use our resources. We want to build on this by establishing an integrated Asian network.
"We will send people from China to Tokyo when they are required, so it will be a truly integrated regional practice."
In London, however, the firm played down the move, saying that a Tokyo office was still in the "thought stages".
The plans by Simmons & Simmons coincide with an initiative by Law Society president Tony Girling to lobby the Japanese later this month in an effort to ease restrictions on foreign law firms. He will make his case before the Ministry of Justice Special Foreign Lawyers Panel on 24 June during a three-day visit to Japan.
Herbert Smith's head of international business Richard Fleck welcomed Girling's initiative, saying existing rules acted as an "impediment to one's ability to practice as a bengoshi [lawyer] in Japan".
Clients, he said, were becoming more receptive to Western firms and the way they deliver legal advice.