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This study examined the activities of aspartate-aminotransferase (AST), alanine- aminotransferase (ALT), gamma-lutamyltransferase (GGT) and lactate-dehydrogenase (LDH) in the blood serum of 45 dairy Simmental cows divided into three groups according to production period. The first group (n = 15) consisted of late pregnant dairy cows, the second group (n = 15) cows in the early lactation, and the third group (n = 15) cow in mid lactation. The significant higher activity (P<0.05) of AST was determined in the early lactation period than in dry period, while enzyme activity in the mid lactation period was higher (P>0.05) than in the dry period. ALT activity showed a lower (P>0.05) serum activities in early lactation cows than in the late pregnant and mid lactation cows. The higher serum activities of GGT (P>0.05) and LDH (P<0.05) were d etermined i n e arly l actation cows than in the late pregnant and mid lactation cows. Research results showed possibility of mild degree of hepatic lesions, probably due to fat infiltration in early lactation cows. Serum AST enzyme activities were significant correlated (P<0.05) with ALT, GGT and LDH activities and may be most sensitive indicato in determining the functional liver state in dairy cows during transition period and mid lactation.