The objective of the present study was to evaluate the effect of rumen-protected methionine supplementation to diets of high producing Holstein dairy cows on milk yield and milk chemical composition. Ninety-nine pregnant Holstein dairy cows were randomly assigned to three nutritional groups to receive a total mixed ration and supplemented with rumen protected methionine (RPM) as; Smartamin (T₁) or Met55 (T₂) or non-supplemented (the control), at 260 days late gestation. Although, the two treated groups, (T₁ and T₂) were daily supplemented with RPM for 30 days pre- and another 30 days post-partum; different experimental groups including the control one were daily provided with 60 g/h choline chloride (Reashour) and 300 cm³ propylene glycol/ h, as an additional supply, during the same treating periods. Different experimental groups were fed a basal ration (16.2 CP % and 70 TDN %) during pregnancy and (16.4 CP % and 74 TDN %) during lactation. Results obtained showed that, supplementing different experimental groups with either Smartamin or Met55 did not improve (p<0.05) cows actual milk yield, 3.5%, fat corrected milk (FCM), energy corrected milk (ECM), milk fat yield nor protein yield kg.h.d^-1. Supplementing Holstein dairy cows with (RPM) did not lead to any significant improvement (p<0.05), neither in animals feed conversion ratio, nor milk chemical composition traits. Animals body condition score (BCS) differed (p<0.05) among different experimental groups due to their yielding productivity in the former breeding season. However, lower milking group tended to have an improved BCS (3.79), but without significant difference with highly producing ones. In conclusion, Smartamin as (RPM) supplement was favored than that of Met55, if there were a necessity to be provided to lactating cows under the local environment.