In the present study, under typical management conditions of dairy farms in Iran, the effect of oral administration of on serum glucose, AST and arginase(indices of liver injuries) of oral monensin was assessed. Thirteen multiparous Holstein cows were blocked into a control and an experiment group from 3 weeks prepartum to 45 days postpartum according the number of their calvings. The groups received similar diets. The experiment group received monensin added to grain mix at 340 mg/head/day during prepartum weeks, 160-480 mg/head/day during first two weeks postpartum, and 350 mg/head/day during days 15-45 postpartum. Blood samples were obtained at days -20 and -10 prepartum, and days 4, 15, 25, 35 and 45 postpartum to determine serum glucose, AST, and arginase. Serum glucose decreased significantly(p=0.025) in the control group from day 10 prepartum to day 15 postpartum. In the experiment group it increased significantly(p=0.049) from the beginning of the experiment to day 35 postpartum. On day 15 postpartum, serum glucose showed a tendency(p=0.07) for significant difference between groups. The level of AST was higher in the experiment group from day 10 prepartum to day 25 postpartum with a significant difference(p=0.011) on day 10 prepartum. There was no significant difference in serum arginase activity between control and experiment groups(p>0.05). Administration of monensin mixed with diet can result in better functions of the liver, increase(or prevention of decrease) in serum glucose during peripartum weeks.