Fifty six Holstein lactating cows (71 days in milk; 35 Kg/day milk production) were employed in a complete block randomized design of repeated measurements. Cows were randomly allocated to two treatments based on their parity. Cows in group 1 were fed a balanced total mixed ration (600 g concentrate /kg DM and 400 g forages /kg DM) with 50 g Rumen Protected Methionine (RPM) per head per day (Methioplus 55%), while cows in group 2 were fed TMR without additive (control group). The experimental period was 40 days with 10 initial days for adaptation. RPM had no effect on milk production, milk composition and dry matter intake. Milk composition namely fat, protein, lactose, solid non fat and total solid percentage did not change by treatment (P>0.05). Cows treated with RPM bore a higher concentration of plasma glucose, and a lower plasma concentration of nonesterified fatty acids (NEFA; P<0.05). Cows in the two groups did not differ in body condition score changes during the experimental periods. It was concluded that RPM increased plasma glucose, decreased NEFA concentration, and can lead to a decrease in the incidence of ketosis and fatty liver in early lactation cows via improving liver function in fat metabolism and gluconeogenesis.