Abstract: Background and Objectives: Ketosis in dairy cow after parturition is a disease in dairy farms chiefly caused by lack of energy. It was examined that the preventative effect of oral administration of propylene glycol and feeding bypass amino acids prospectively on ketosis in dairy cows. Materials and Methods: Sixteen Holstein cows, serum total cholesterol concentrations <87 mg dL–1 (72±10 mg dL–1) at 2 weeks before parturition that were at risk of developing ketosis after parturition, were randomly assigned to 3 groups. Seven cows were not treated (NT group), 5 cows were orally treated with 90% propylene glycol upto parturition at 250 mL/day/head for 10 days (PPG group) and 4 cows were given a combined treatment of propylene glycol in the same way as the PPG group and were also fed bypass amino acids at 400 g/day/head from -7-14 of parturition for 21 days (PPG+BAA group). The results of 3 groups for incidence of ketosis, treatment days, blood examination (serum 3-Methylhistidine, NEFA, TCho, BUN, Alb, AST, GGT) and BCS were compared. Numbers of cows with ketosis were analyzed by chi-square test. Results: The incidence of ketosis in the NT group was higher than in the PPG+BAA group significantly (p<0.05). The serum 3-Methylhistidine concentration in the NT group was higher than in the PPG+BAA group at 2 weeks after parturition (p<0.05). The serum GGT activity in the NT group was higher than the normal range at 0, 2 and 4 weeks of parturition and was significantly higher than those in the other two groups at 2 weeks after parturition (p<0.05). Conclusion: These findings suggested that administration of propylene glycol and feeding bypass amino acids controls the acceleration of body protein degradation and prevents liver dysfunction. This is an effective method for prevention of ketosis in dairy cows.