The present work was carried out to investigate the effect of semen quality of bulls on repeatability and milk yield of cows. One hundred cows from a private dairy farms 360 kms southern Khartoum city were suffering from repeatability and poor milks yield Veterinary medical diagnosis was carried out for the cows, no ventral disease or physiological aspects were observed, semen ararnination was done to the sires (six), four sires out of them had aspermia, while the other two sires have low fertility rate (less than 50 %). The sires replaced with proven ones , hence the cows onceived and became pregnant, calved and gave abundant milk. The present work research found that there is positive effect of semen eva!uation on conception and on milk yield. It could be the research recommended that monthly semen evaluation arid brucella test to must be carried out minimize to avoid the repeatability and indirectly to increase yield the poor milk of the cows. Keywords: Bull, Semen, Repeatability, Milk Production INTRODUCTION One of the most important factors to be examind for bull fertility is semen evaluation (Setchefl, 1977). Bull fertility usually considered as a measure for sire reproductive efficiency Bearden, and Fuquqa (1987) proven sire is very important for dairy fanning arid ¡t should be mature enough to copulate, healthy, has moderate size, from good dairy breed, more sexually aggressive, more quickly moving around and copulate more often before exhausted (Webster, 1987). Semen should be examined and evaluated in vitro before insemination. The factors cause deffect in sperm viability such as testicular. Degeneration, lorchites, epididymitis, heat stress, and inadequate feed. So this study aime to study the effect of semen quality on repeatabOity and milk production of cows. MATERIALS AND METHODS One hundred cows and 6 Bulls from a private farm (360 kms southern Khartoum were kept examined for the following: 1. Brucella test: (Ring test). 2. Semen quality (Semen to be examined to recognize the viscosity, colour, mortality, volume concentration and fertility).