In the first experiment, RSK (rubber seed kernel) contained greater amounts of crude protein, ether extract and gross energy, and lesser nitrogen-free extract, natural detergent fiber, acid detergent fiber, hemicellulose, cellulose and lignin than RSC (Rubber Seed Cake with shell). RSK and RSC were similar in ash, Ca, P, HCN and tannin content, but the free gossypol was higher in RSC than RSK. In the second experiment, the digestibilities of dry matter, organic cell wall constituents and gross energy were higher (p<0.05) in RSK than those in RSC, while that of crude protein was similar. The N retention in terms of related N per N intake or retained per digested N were similar in both ruzy hay + RSK and ruzy hay + RSC. In the third experiment, the animals fed with ruzy hay alone lost weight. When the ruzy hay was supplemented with concentrate, both body weight gain and feed efficiency increased (p<0.01).However concentrate intake was inversely related to RSK in concentrate. Increasing level of RSK in concentrate mixture was associated with linear decline in concentrate intake, totalfeed intake abd simultaneous lineal decrese in body weight gain and feed efficiency. The goats fed with all ruzy hay diet had greater (p<0.05) white blood cells, hematocritand hemoglobin than those fed with ruzy hay supplemented with concentrate ration. Also, red blood cells, hematocrit and hemoglobin linearly decreased when the level of RSK in concentrate increased. The protein deficiency symptoms were observed in goats fed with ruzy hay as a sole diet. In the fourth experiment, the animals fed with ruzy hay alone gained weight. Supplementataion of concentratesignificantly increased feed intake, body weight gain and feed efficiency but did not affect cost of feed per kg weight gain. Increasing level of RSC in concentrate caused linear decline in body weight gain and feed efficiency. The total plasma protein linearly increased as the level of RSC in concentrate increased.