Later, he was involved in conclusion of the Anglo-Japanese Alliance, the negotiation with Russia and the diplomacy in the outbreak of the Russo-Japanese War under KOMURA, Minister of Foreign Affairs and played a leading role in Komura's diplomacy by drawing up the sentence of proclamation of the Russo-Japanese War and accompanying to Treaty of Portsmouth between Japan and Russia.
その後、小村外相のもとで、日英同盟締結、日露交渉、日露戦争開戦外交に関わり、日露戦争宣戦布告文を起草、日露ポーツマス条約に随員として出席するなど、小村外交の中心的役割を担った。