Abstract: DNA Ploidy and cell cycle in 111 cases of breast lesion and 95 cases of Para—lesion tissue were measured using Flow Cytometry. The difference of DNA Ploidy Patterns and cell cycle between benign and malignant breast diseases was analysed and their value for diagnosis of breast malignancy was studied. The result showed that,aeuoploidy rate of breast cancer cases was 78%and 89.75 %of aeuoploidy cases were multiploidy pattern.2 cases of breast hyperplasia(11.11% )and 11 cases of breast fibroma (25.58% )showed aeuoploidy pattern.However,there were not any multiploidy patterns appeared in benign breast disease and para —lesion tissue.Analysis of cell cycle showed that proliferous activity(SPF or PI)of breast cancer and para—cancer tissue was much higher than that of benign breast diseases. The results suggested that DNA multiploidy pattern and high proliferous activity could be used for identification of benign and malignant breast diseases.