Milk vetch is a popular and tranditional green manure for paddy soils in South China. In order to study the decomposition and transformation of the nitrogen of milk vetch in soil, plot, microplot and pot experiments were carried out in 1980 on paddy soils derived from red earth in Jinhua County of Zhejiang Province. The milk vetch and urea labelled by ¹⁵N were used in microplot and pot experiments.Results obtained from the. experiments are summarized as follows: (1) The decomposition rate of milk vetch, i.e. the percentage of the loss o.f dry matter ranged from 64-70% during the growing season of the early rice (85 days), and 30% of C was remained in soil after harvest. (2) The recovery rate of N in milk vetch by the early rice estimated by difference method between plots ranged from 24-42%. The effect of 22.5 t./ha of milk vetch (fresh matter) on the yield increase and recovery rate of N was greater than that of 11.25 or 33.75 t./ha of milk vetch. The results obtained by difference method in field experiment were approximately equal to those obtained by ¹⁵N-labelled method in pot experiment. (3) The effect of milk vetch applied on early rice in red earth was significant, but the recovery of residual N in soil by late rice was only 7-8%. (4) The uptake peak of N from milk vetch and urea by early rice. appeared at the tillering and jointing stages. Although N recovered from milk vetch and urea amounts to 3000, the fates of the milk veth-N and urea-N in soil are different. About 50% of milk vetch-N was still remained in soil, while 50% of urea-N was lost. This indicates that the milk vetch can promote not only the accumulation, but also the decomposition of the N in soil, and it may also accelerate the regeneration and circulation of the organic N in soil.(5) Although the ezperi.ment has shown that about 50-80% of the total N in plant was come from the mineralized soil-N, and only 10-25% took up from the N of milk vetch and urea, it is of great significance for the yield increase of early rice to apply milk vetch and urea so as to meet the need of N in its peak growing stage.