 Yamaza was part of the Japanese delegation which negotiated the Treaty of Portsmouth.In this context, some Korean scholars assert that Yamaza played a notable role in calling for incorporation of Liancourt Rocks within Japanese territorial claims.In 1908, Yamaza was councillor of the Japanese embassy in Great Britain, with responsibility for planning of Japan's participation in the London Naval Conference (1908–1909) and the Japan–British Exhibition in 1910.