U-Thong mungbean seeds were first harvested when they attained field maturity, 58 days after planting. Three subsequent harvests were made at weekly intervals. It was found that weathering reduced seed yield and quality. Yield losses were manifested by reductions in szed weight and threshing percentage. Overripe pods became detached from the plants. Quality losses included decline in seed germ inability and vigour. Seed dry weights for the first, second, third and fourth harvests were 54, 53, 49 and 40 mg/seed, and germinability was 98%>, 94%, 85% and 79%, respectively. Seedling emergence declined from 93% to 89%> to 82% to 70%. Shoot dry weight showed a significant decline with each harvest interval but root dry weight showed no significant difference. Seeds o f later harvest showed a higher degree o f infection by seed borne fungi, especially, Fusarium spp. Infection by Aspergillus spp. and Curvularia spp. were also observed. The severity o f infection increased after the onset o f the rainy season.