This study was conducted to investigate the effects of some environmental factors on milk yields of Simmental cattle reared on private farms in Kayseri. Since the study took place on various farms, a common feeding and managemental program was not employed. The measurable factors of the environment such as the farm type, year and season, and lactation turn were investigated. The data was analysed statistically by using the least squares means method to measure the effect portions of environmental factors and contrast-test and GLM procedure in SAS program pack were used to compare the values. The lactation milk yield of Simmental cattle in the study was 3506.20 kg, 305 days milk yield was 3412.08 kg, lactation period was 312.71 days and dry period was 70.77 days. Effects of farm type and season were significant (P<0.001) on the real and 305 days milk yield, and season was significant (P<0.05) on the duration of lactation. All the factors were not significant on the dry period.