The hypothesis behind this study was that urea plus Ca(OH)2 treatment would improve the nutritive value of rice straw and improve dry matter intake, digestibility, rumen ecology and microbial protein synthesis in beef cattle. Therefore, the objective of this experiment was to determine the effects of urea plus Ca(OH)2 treated rice straw on the nutritive value of rice straw and dry matter intake, digestibility, rumen ecology and microbial protein synthesis using rumen-fistulated beef cattle.