Field experiments were conducted to investigate persistence of Chinese milk vetch(CMV) seed under naturally reseeded CMV-rice cropping systems during the period of 2007~2009. Persistence of the CMV seeds were evaluated in the naturally reseeded CMV-rice field on different tillage methods and soil depths based on the seed number recovered and the seed longevity in soil. Field observation in the naturally reseeded CMV rice field showed that as many as 917~2,185 CMV seeds m-2 were found from 0~15cm soil depth in the rotary tillage and 250~10,105 CMV seeds in minimum tillage rice cultivation in autumn. The recovered seed germinated 25~33%, 23~43% but still had high percentage of hard seed having 64~72% and 51~77%. Field experiment showed that the CMV seedling still emerged even after 2 years of continuous destructive killing of emerged CMV plant by rotary tillage in naturally reseeded CMV-rice field, indicating that CMV seeds persistent at least two years in rice field.