Four Thai native beef cattle were randomly assigned according to a 4 × 4 Latin square designto evaluate the effect of urea calcium sulphate mixture (U-cas) levels in feed block onfeed intake, apparent digestibility of nutrients and rumen fermentation fed on rice strawbased diet. The four dietary treatments were different levels of U-cas supplementation infeed block at 0, 120, 150 and 180 g/kg dry matter (DM),