This study discusses Sir Horace Seymour's role in the development of Sino-British relations in the critical years from 1942 to 1946, his assessment of Chinese military, political and economic conditions, and his diplomatic efforts and contribution to the emergence of a new vision in British policy towards China. As is emphasised in this thesis, Seymour arrived as British ambassador to China in February 1942 at a time when British arms had suffered a succession of serious reverses in Hongkong, and Malaya, and when British prestige in the Far East was at a low ebb. By his tact, dignity and courtesy, and particularly his spirit of equality, he gained the trust and respect of all Chinese with whom he came in contact, and contributed in no small measure to the gradual restoration of British prestige in China and to the high degree of cordiality attained in Sino-British relations in the later stages of the war. He became, through his ready grasp and sympathetic understanding of Chinese problems, a reliable interpreter to the British government of Chinese needs and aspirations, and therefore contributed a great deal to British policy towards China both during the war and in the immediate post-war period. He met with, however, constraints both from official and unofficial circles in Britain, owing to the different opinions existing in Britain. Nevertheless, there was always room for Seymour to manoeuvre in the formation of British policy towards China.