Abstract: This research aimed to study the effects of cassava pulp mixed with urea Gelatinizes (Caspurea) on productive performance of Thai native x Brahman beef cattle. Four yearling Thai native x Brahman beef cattle with average live weight of 154.7±26.8 kg were used in a 4x4 Latin square arrangement of treatments with 4 periods, each period consisted 21 days. The treatments were levels of Caspurea replacement for soybean meal in concentrate at 0, 25, 50 and 75%. Concentrates were formulated to contain 14% CP and were fed at 2.0% BW. All animals were fed ad libitum urea treated rice straw as roughage. The results showed that total dry matter intake (5.5, 5.5, 5.2 and 5.3 kgDM day^-1; p>0.05) was not significantly different among dietary treatments. DM digestibility (71.2, 72.1, 71.2 and 67.7%; p<0.01) was lowest in 75% replacement diet. DM digestibility decreased linearly (p<0.01) and quadratically (p<0.01) as the level of Caspurea increased. Ruminal ammonia-N concentration (8.5, 8.8, 9.5 and 13.3 mg%; p<0.01) was highest in 75% replacement diet and increased linearly (p<0.01) and quadratically (p<0.01) with increasing the level of Caspurea. Moreover, linearly (p<0.01) and quadratically (p<0.01) decreases in TVFAs (127.4, 123.6, 119.8 and 96.4 mM L^-1; p<0.01) observed were (total volatile fatty acid) reflecting increases in level of Caspurea. Increase in level of Caspurea caused linearly (p<0.01) decrease in bacteria (2.6, 2.5, 2.5 and 2.4x10¹⁰ cell mL^-1) and protozoa populations (2.2, 2.2, 2.1 and 1.9x10⁵ cell mL^-1). Nitrogen absorption (65.5, 64.7, 60.6 and 57.7 g day^-1) were also lowest in 75% replacement diet (p<0.01) however, among 0, 25 and 50% replacement groups were not differ. With increasing the level of Caspurea, N absorption was decreased. Nitrogen retention (%N intake) (24.1, 23.6, 25.3 and 13.6%N intake) tended to increase in 50% replacement diet (p = 0.05) while, in 0, 25 and 50% replacement diet groups were not differ, moreover, N retention tended to decreased linearly (p = 0.08) as the level of Caspurea increased. Blood urea nitrogen (22.5, 23.2, 23.3 and 24.6 mg%; p<0.01) was highest in 75% replacement diet and BUN increased linearly (p<0.01) with increasing the level of Caspurea. These results indicated that 50% replacement diet by Caspurea for soybean meal in concentrate has positive effects on Thai native x Brahman crossbred beef cattle production.