Abstract: Four Simmental steers(average BW 420 kg, aged 2.5) cannulated at the rumen consuming a corn straw diet were used in a 4×4 Latin square design and supplemented with four levels(0, 0.45, 0.90 and 1.8 g/head/d) of supplemental lanthanum chloride to evaluate the effects of different lanthanum chloride levels on ruminal pH, NH3-N, VFA, nutrients degradability and purine derivatives of urine. At the 0.9 g/head/d lanthanum chloride level, ruminal pH and NH3-N concentrations were decreased significantly (P<0.05), the effective degradability of DM, OM, NDF and ADF of corn straw were increased significantly (P<0.05), soybean DM, OM and CP effective degradability were not affected by lanthanum chloride supplementation, but ruminal propionate, TVFA and purine derivatives of urine concentrations were increased significantly (P<0.05), acetate/propionate decreased significantly (P<0.05). The supplementation of lanthanum chloride had passive effect on rumen, the optimum lanthanum chloride supplemented dose was 0.9 g/head/d.