Effects of recombinant bovine somatotropin {rbST) treatment on buffalo milk production and composition were studied under the Egyptian dairy farm conditions, Thirty—six buffaloes delivered during the same season were assigned to either control (n=16) or rbST treated groups (n=20). The treated animals were subcutaneously injected biweekly by 500 mg of rbST over a period of five months of lactation! starting at 50 days postpartum. The results showed that rbST treated buffaloes produced significantly (P<0.01) higher average daily milk yield than controls. Average daily milk yield of the experimental period were 8.57:0.39kg and 10.561035 kg for control and treated buffatoes. respectively. Treatment with rbST did not affect buffaloes milk composition (fat. lactose, total solids and solids non fat contents). while it significantly affected(P<0.01) the milk protein %. A slight significant (P<0.05) effect on fat percentage was found during different phases of lactation between treated and control animals (at 5‘“ month of Iactation).Percent of milk protein was significantly(P<0.01) affected by the interaction between treatment and month of lactation. Treatment with rbST had a significant (P<0.01) effects on percentage of fatty acids in milk fat which characterized by clearly higher percent of Myristic acid (014.00). Oleic acid ((313110) and Stearic acid (C1330). The percentages of short chain (< 012100) and medium chain acids (Cmflo-Cmoo) in milk fat were lower in treated buffaloes compared to controls. it was concluded from this study that treatment of dairy buffaloes with rbST could significantly increase their milk yield without significant changes in milk composition except for higher content of long chain fatty acids