Abstract: Fifteen lactating buffaloes after seven days post-parturition were divided randomly into three groups (of 5 animals each) to study the effect of adding By-Pass Cement Dust (BCD) level to the buffalo’s diets on the coefficients of nutrient digestibility and milk yield and composition using complete random block design experiment with 90 days period. The control group was given a basic diet consisting of (60% Concentrate Feed Mixture (CFM): 20% berseem clover: 20% rice straw), the second and third groups were fed the control ration plus 7.5 and 15 g/head/day BCD, respectively. The CFM for each animal was offered individually once daily at 8.00 am, while berseem clover and rice straw were offered at 10.00 am. Individual milk samples were collected every two weeks of the experimental period for chemical analysis. After 4 h of the morning meal, grab samples and blood serum samples were collected in the last day every month for chemical analysis. Nutrients digestibility coefficient of organic matter, crude protein and crude fiber were significantly higher with animals fed low level followed by high level of BCD and then control. Also, dry matter, ether extract and nitrogen free extract digestibilities followed the same trend while the effects of treatments failed to be significant. Supplementation of low level of BCD to buffaloes rations increased yields of milk (p<0.05), 4% FCM (p>0.05) and milk constituents (p>0.05) compared with other treatments. Milk fat, protein and lactose contents were insignificantly increased with animals fed BCD compared with control. While, total solids, ash and solids not fat contents were not differed among treatments. Milk P, Mg and K contents were significantly higher with animals fed BCD compared with control. Feed efficiency as Milk yield/dry matter intake (DMI) (p<0.05) and FCM/DMI (p>0.05) were higher for animals fed BCD than that fed control. Blood serum total protein, urea and glucose were higher (p<0.05) in animals fed on low BCD supplemented rations, while, other blood serum parameters were not affected by treatments. Also, blood serum Ca, Na and Fe were significantly higher in animals fed on low BCD supplemented rations compared with control. It could be concluded that low BCD supplementation (7.5/head/day) to diets improved nutrients digestibility coefficients, milk yield and milk constituents than other treatments.