1.Total reductive substances and active ferrous compounds were determined in soil:1) of green-manured and not green-manured control,both under rice crop;2) under rice crop and uncroped control,both after green-manuring.2.Total soil reductive substances determined within 15 days after green-manuring were significantly higher than not green-manured control.The deferences decreased with time and were caused chiefly by the active reductive substances mainly in organic form.3.Within 54 days after green-manuring,the ferrous content of soil varied within 2.6-3.5 milli-equivalent per 100 g.During the earlier stages of rice culture the ferrousoon increased progressively with the progress of the decomposition of green-manure.4.Before tillering,the total reductive substances in the top 0-5 cm soil layer were higher than in underlying 5-15 cm layer;after the tillering stage,the relation was reversed.5.The experiment results point out that the excessive accumulation of active reductive substances might be the cause of seedling-rot and death of seedling when seedlings are transplanted within a few days after green-manuring.