This article explores the activities of the Research Neighborhood Groups (kenkyu tonarigumi) in the context of the mobilization of science and technology during World War II, and throws light upon their influence on research collaboration in postwar Japan. Although research collaboration has recently attracted academic attention as a factor in the competitive ability of Japanese industry, its history has not yet been fully researched. The Research Neighborhood Groups scheme played a unique and symbolic role in research collaboration activities of various kinds during the War because the aim was to organize research collaboration over the length and breadth of the country. It was planned by the Cabinet Technology Agency and carried out by its extra-governmental organization. The groups were in principle organized by young and promising researchers on the same special subject. The total number of researchers enrolled rose to about 3,000. Three typical examples, the vacuum tube, and vitamin and statistical quality control groups, clearly had decisive influence on the research collaboration activities which took their place after the war. The activities of the Research Neighborhood Groups scheme built connections between researchers belonging to various institutions which went on to provide a secure basis for successful research collaboration in postwar Japan.