Abstract: This experiment aimed to study the effects concentrate mixed with Extrusion-processed Mixture of Cassava Pulp and Urea (EMCPU) and varying levels of Ruminal Undegradable Protein (RUP) on productive performance of crossbred (Thai Native x Brahman) beef cattle. Four cattle with an average bodyweight of 175.5±18.6 kg) were used in a 4x4 Latin square arrangement of treatments with 21 days periods. The treatments were the concentrate mixed with EMCPU and varying levels of RUP at 30, 35, 40 and 45% (T1, T2, T3 and T4). Animal were fed at 2.0% BW of concentrate mixed and all animals were fed ad libitum with urea treated rice straw as roughage. The results showed that dry matter intake increased linearly (p<0.01) as the level of RUP increased. Moreover, organic matter digestibility increased linearly (p<0.05) with increasing the level of RUP. Ruminal ammonia-N concentration was highest in 30% RUP. In addition, linearly decrease in ruminal ammonia-N (p<0.01) reflected increases in level of RUP however, at 45% RUP, NH3-N was increased quadratically (p<0.01). Total volatile fatty acid (94.3, 113.25, 116.7, 112.1 mM L-1; p<0.01) increased linearly (p<0.01) as the level of RUP increased. However, at 45% RUP, TVFAs decreased quadratically (p<0.01). Increase in bacteria and protozoa populations reflected increased in level of RUP from 30-40%. However, bacteria and protozoa populations were decreased (quadratically, p<0.05) as the level of RUP increased from 40-45%. Nitrogen absorption was not significantly different among dietary treatments. Nitrogen retention (20.9, 19.7, 31.0, 21.5 g day-1; p<0.05) was highest in 40% RUP and tended to increase as level of RUP increased however, at N retention at 45% RUP tended to decrease (quadratically, p = 0.1). These results indicated that 35% CP from EMCPU replacement for RUP levels at 40% in concentrate have positive effects on crossbred Native x Brahman beef cattle production.