Breast cancer is the second most common cancer among females in rural areas of our country. It constitutes around 20-25% of all female cancers in India. ABO blood group has been observed to be associated with gastric and pancreatic cancer, but its association with breast cancer is unsure. AIMS & OBJECTIVES:1.To find any association between breast cancer and ABO blood group. 2. To know the frequency and risk of each blood group in relation to patients with breast cancer. This study was conducted in the Department of Surgery, Tirunelveli Medical College. Ethical committee approval was obtained.100 breast cancer cases were taken and 100 healthy women with no reports of breast cancer were taken as controls. Blood grouping was done by Standard Agglutination method. Association of ABO blood groups and breast cancer was found out with Odd Ratios (ORs) with 95% Confidence Interval (CI). ABO blood group distribution among patients with breast cancer was as follows: Group A- 39%, Group O-31%, Group B- 26% and Group AB- 4% Among 100 healthy controls, ABO blood groups percentage was: Group O- 32%, Group A- 15 %, Group B- 46%, and Group AB- 7%. There is significant association between blood group A and breast Cancer since the p value was <0.05This study showed that there is strong association between ABO blood group system and female breast cancer and the highest risk for breast cancer was in blood group A and minimum in blood group AB.