Abstract: Objective To analyze the effect of menstrual cycle on intraoperative blood loss (IBL) in females who underwent total hip arthroplasty (THA). Methods One hundred and ffty regularly menstruating females diagnosed as osteonecrosis of the femoral head (ONFH), osteoarthritis of hip, or congenital dysplasia of acetabulum (CroweⅠ-Ⅱ) were retrospectively enrolled in this study. They all underwent unilateral THA between August 2010 and March 2016 in Chinese PLA General Hospital. Age, height, weight, body mass index (BMI), preoperative hemoglobin and coagulation test results (PT, APTT, TT and PLT) were collected and analyzed. The average age of these patients was (31.23±5.64) years with a range of 19 to 39 years. To minimize the effect of different length of menstrual cycle of these patients, day in menstruation (t) to length of menstrual cycle ratio (T) (t/T ratio, range:0.00-1.00) was calculated for each individual. Patients were classifed into four groups according to menstrual cycle phase:1)menstrual group (0< t/T ≤ 0.20, n=22), 2) follicle group (0.21 ≤ t/T ≤ 0.59, n=68), 3)ovulatory group (0.60 ≤ t/T ≤ 0.79, n=29) and 4) luteal group(0.80 ≤ t/T ≤ 1.00, n=31). The clinical data and difference of IBL in the four groups were analyzed by one-way ANOVA (for normal distribution data), Kruskal-Wallis H test (for non-normal distribution data) or Chi-square test (for enumeration data) accordingly. Results There was no signifcant difference in patients' clinical data (age, height, weight and BMI)between 4 groups. Although TT and PLT were signifcant differences in the four groups (P=0.043 and P=0.038, respectively), they were still in normal range. The IBL were 250.00 (200.00, 300.00) ml in follicle group, 300.00 (200.00, 400.00) ml in ovulatory group, 300.00 (200.00, 350.00) ml in luteal group, 225.00 (200.00, 300.00) ml in menstrual group. The difference of IBL between four groups was not statistically signifcant (P=0.747). Conclusion Females would not suffer more IBL when underwent THA in the menstrual phase.