Needham's interest in China dated from contact with Chinese colleagues at Cambridge from the mid 1930s. He taught himself Mandarin Chinese and began to study Chinese science and history. In 1939, responding to appeals for assistance, he and his wife offered to go to China to help in the reconstruction of Chinese science. Meanwhile Needham was active in seeking support for Chinese academics in the UK.
Early in 1942 Needham and E.R. Doods, Regius Professor of Greek at Oxford, were invited to visit China under the auspices of the British Council. They arrived in the autumn of 1942, Needham travelling via the USA. In China Needham was made Head of the British Scientific Mission and later Scientific Counsellor to H.B.M. Embassy at Chungking (then the 'acting-capital' of China). Under the auspices of the British Council Needham established the Sino-British Science Cooperation Office (SBSCO) and became its first Director. The SBSCO was responsible for assessing the needs of Chinese scientific, technological and medical institutions and researchers, and facilitating the supply of equipment, medicines, books and journals to China. Needham made several journeys through China, visiting many institutions to assess for himself the needs of Chinese research and teaching centres. He also gave many lectures on a variety of subjects from biochemistry to world politics. He was later joined by his wife Dorothy who was appointed Associate Director of the SBSCO.
In a letter of 22 January 1946 (C.32) to A.C. Chibnall Needham set out the logistical achievements of the SBSCO:
'...with 17 scientists (5 British, 12 Chinese), not all present at one time... we visited 300 laboratories, covering over 25,000 km journeys; we flew in by RAF over the hump [£]60,000 worth some tons of scientific equipment for Chinese scientists; we flew in some 7,000 scientific and technical books worth many millions of Chinese $, and microfilm and actual copies of 200 leading British scientific journals. We sent 150 original MSS by Chinese authors to the west for publication, and 200 Chinese scientific journals. Exchanges of information were innumerable'.
In addition to his role as Director of the SBSCO, the Chinese Government appointed Needham adviser to the National Resources Commission, the Chinese Airforce Research Bureau and the Chinese Army Medical Administration. He was also warmly received by the Chinese scientific community and elected to a number of academies including the Academia Sinica and Peiping National Academy. Needham left China in February 1946. In October 1947 Chiang Kai-Shek awarded Needham the Order of the Brilliant Star with Cravat in recognition of his work in promoting good relations between Britain and China. It was presented to Needham by the Chinese Ambassador to Britain in July 1949.
Needham wrote regular reports on the organisation and state of science in China for Nature and in 1948 edited the book Science Outpost which described the work of the Sino-British Science Cooperation Office. Needham's experiences in heading the SBSCO, an experience in scientific cooperation between nations, was crucial to his formulation of plans for wider international science cooperation within the new UNESCO.