Background: Menstruation is a phenomenon unique to females and nearly universal experience in women's lives and is poorly understood .It is characterized by co-ordinated sequence of hormonal changes but the changes occur in haemotological parameters, have not been clearly established. Objective: To compare haematological parameters in different phases of menstrual cycle. Materials & methods : The present study was carried out on 92 healthy female medical students in the age group of 18 to 23years with normal menstrual cycle of 27-33 days. Various haemotological parameters were studied during menstrual, Proliferative and Secretory phases of menstrual cycle. Result: The Red blood cell count, hemoglobin concentration, total leucocyte count, Differential leucocyte count, total platelet count showed no significant changes during various phases of menstrual cycle. The Erythrocyte Sedimentation Rate was significantly (P<0.01) higher in menstrual phase compared to proliferative phase. Conclusion: The changes in the present study may have significance in terms of normal reference interval on menstrual cycle and their impact on health status.