伍廷芳是晚清著名的外交家，是近代中國向西方尋求真理的代表人物之一。然而，以往的研究，忽視了伍氏與日本之間係。本文採用日本外交檔案中原始記錄，揭示了伍廷芳研究中被人們忽略的一個重要方面。 早在甲午戰爭中，伍廷芳作為《馬關條約》談判的頭等參贊，開始與日本方面有較多接觸。回國後，伍氏又向日本駐天津領事荒川巳次及駐京公使林董，多次提供清廷上層不同政治派別對和戰的態度，以及彼此間的矛盾與裂痕等情報，並對中國前途悲觀失望，以為中國會四分五裂，走向滅亡。伍廷芳還試圖藉日本戰後之威力來恢復李鴻章在戰爭中失去的權力和地位。公然聲稱，如果李鴻章能繼續有所作為「實彼我之幸福，兩國之大利也」。爾後，伍延芳由美國出使歸來，又再度向駐京公使內田康哉泄露清廷內部政要秘聞，揭露了清廷內部長期存在著一個親俄黨，聯芳即其代表人物，以及光緒皇帝生前之危險處境，並試圖要日本公使及夫人向慈禧進言，勸慈禧拔擢伍氏等到關鍵崗位等。 日本檔案中所保留的這些情報在今天看來，似乎已是人們共知的情事，而在當時日本外交官卻對此類情報極為重視，他們都將伍氏談話認真整理後系統向外務大臣報告，然後，外務省又將它們大多呈送給總理大臣過目。 本文具體分析了伍廷芳向日本提供情報的原因，主要是受李鴻章等人政策之影響，以及伍氏本人對封建制度的厭惡和對日本抱有不切實際的幻想所致。本文揭示日本機密檔案中這些罕為人知的史料，不是要否定其歷史功績，而是希望正確認識中國近代史上這個重要歷史人物。

Wu Tingfang was a very famous diplomat in late Qing, was also one of pioneers seeking truth from the West. Earlier studies on him neglected Wu’s relationship with Japan. This article is written according to the original records in the Japanese Foreign Office Archives, and reveals one important aspect which so far not known to the public. After the Sino-Japanese War, being the first attaché in the Chinese Negotiation Delegation, Wu began to have frequent contacts with the Japanese. Later Wu returned to China and paid visits to the Japanese Consulate-general in Tianjin, Kiji Arakawa, and the Minister, Tadasu Hayashi, many times, and reported to them about situation of the power struggle among the different cliquesin the high level of the Qing bureaucracy. He also provided some information on the Qing attitudes toward war and peace. Wu also showed pessimism towards the future of China, thought China would split up and be eventually destroyed. Wu sought the help of post-War victorious Japan to restore Li Hongzhang’s power and status lost during the War. Wu even c1aimedpublicly that if Li should regain his power, it would have “great happiness and benefits for both of our two countries.” Wu was later appointed as the Minister to the United States. After he returned, again he revealed to the Japanese Minister Yasuya Uchida on the information regarding the pro-Russia faction in the Qing Court and Lian Fang was a leader. He reported the precarious situation of the Guangxu Emperor. He also attempted to persuade the Japanese Minister and his wife to put in a good word for him in front of Empress Dowager Cixi and elevate Wu into high position... The information as revealed in the Japanese archives is well known today. But at that time the Japanese diplomats took it very seriously. They carefully sorted out and systematically presented to the Minister of Foreign Affairs. In turn, the Ministry of the Foreign Affairs presented most of the information to the Premier of Japan. This article specifically analyzes the reasons behind Wu’s providing information to the Japanese. It was mainly because Wu was influenced by Li Hongzhang’s policies, and Wu’s abhorrence toward the Chinese feudalistic system, together with his impractical fascination towards Japan. This article unearths those almost unheard-of materials from the Japanese secret archives, in the hope that, rather than denying Wu’s historical contribution, but understanding correctly this important figure in modem China.