Four Thai native beef cattle were randomly assigned according to a 4 × 4 Latin square design to evaluate the effect of urea calcium sulphate mixture (U-cas) levels in feed block on feed intake, apparent digestibility of nutrients and rumen fermentation fed on rice straw based diet.The four dietary treatments were different levels of U-cas supplementation in feed block at 0, 120, 150 and 180 g/kg dry matter (DM), respectively. The present results revealed that rice straw intake increased with the increasing levels of U-cas inclusion in the feed block.