The current work was carried out on two hundred of Baladi and crossbred (Baladi x Friesian) cows to estimate effect of season of calving and mastitis on the reproductive performance under the environmental conditions of Aswan governorate in south Egypt. The cows follow up after one month post-partum and the California Mastitis Test was performed for all experimental cows by (California Mastitis Test). According to season of calving the cows were divided into two groups. The first group that calved during the cold season and the second group calved during the hot season. The cows Baladi and crossbred cows that calved during the cold and hot seasons were divided into two groups according to suffering of mastitis healthy cows and cows with mastitis (sub-clinical mastitis). The results demonstrated that the interval from calving to first service was longer (75.56± 12.3, 82.63±7.51days) (P <0.05) in cows that calved during the hot season than cows that calved during the cold season ( 65.71± 14.27, 74.58± 8.94 days) in healthy Baladi and crossbred cows respectively. The interval from calving to the first service was longer in Baladi cows that suffer from mastitis (78.96± 15.08, 84.95±8.4 days) compared with healthy cows (65.71± 14.27^, 75.56± 12.3days) during the two seasons cold and hot respectively. The interval from calving to the first service was longer in crossbred cows that suffer from mastitis (85.89± 6.81, 87.09±7.11 days) compared with healthy cows (74.58± 8.94, 82.63±7.51 days) during the two season cold and hot respectively. The interval from calving to conception was greater in cows that calved in the hot season (96.93±10.66, 101.26±13.65days) (P <0.05) than cold season (90.38±11.44, 93.16±11.37days) in healthy Baladi and crossbred cows respectively. The interval from calving to conception was higher in cows with mastitis than healthy cows in Baladi and crossbred cows in two seasons. Number of services pre conception were greater in Baladi  and crossbred cows that suffer from mastitis (2.1±0.62, 2.05±0.22  and 2.08± 0.63, 2.13± 0.67 services) compared with healthy cows (1.95± 0.58, 1.89±0.42 and 2.0± 0.63 , 1.92± 0.67 services) during the two season cold and hot respectively.  Conception rate in Baladi and crossbred cows that suffer from mastitis was lower (37.9^, 15.0, 15.8and 16.1%) compared with healthy cows (66.7^, 36.7^, 66.7and 42.1%) during the two season cold and hot respectively. The percentage of mastitis cases were more frequent in cows during the cold season (58, 76%) compared to hot season (40, 62%) in Baladi and crossbred cows respectively. The rates of short estrous cycles were higher in cows with mastitis during the hot season (42.9, 38.5%) than cold season (33.3, 25%) in Baladi and crossbred cows respectively. The present study clarified that there is a negative effect of hot season and mastitis on the reproductive performance of Baladi and crossbred cows under the environmental conditions of south Egypt. Thus, the present study recommended must preparing effective defense programs in order to decreasing proportion of infection by mastitis for betterment the reproductive performance of Baladi and crossbred cows especially during the hot season of Aswan governorate