Abstract: The effects of soybean frog-eye leaf spot on yield and quality were investigated with different disease degrees in leaf,pod and seed infection.The results showed that this disease reduced yield mainly due to the reduction of leaf area,increase of respiration and decline of net photosynthetic rate.However,studies indicated that there was a positive relationship between seed relative protein content and seed diseases infected degree, and there was no significant effect on fat content.Both absolute seed protein content and fat content were significantly affected by seed disease degree.Some measures for controlling the disease were also proposed.