An experiment was conducted to evaluate the effects of nitrogen supplementation through urea-molasses multinutrient block (UMMB) on the performance of dairy cows fed good quality forage based diets with rice straw as a night feeding. A total of 10 multiparous crossbred dairy cows in their early lactation were grouped into two categories based on their breed, parity, body weight, milk yield, milk fat and protein contents and daily fed a chopped CO-3 grass (Pennisetum purpureum ${ imes}$ Pennisetum americanum; hybrid Napier) ad-libitum, 1 kg of dairy cow concentrate feed during the day time and 5 kg of rice straw (dry matter basis) at night as the basal diet (control) for 5 wk. In addition to the basal diet, the treatment group received 300 g of crushed UMMB daily throughout the experimental period. Cows were milked twice daily and the milk yields were recorded. Milk and feed samples were collected weekly for chemical analysis. Supplementation of UMMB had no significant effects (p>0.05) on straw intake, daily milk yield, contents and yields of milk constituents such as milk fat, protein, lactose and solids-non-fat. In addition, milk urea nitrogen content were not affected (p>0.05) by UMMB supplementation. However, numerical increments in all the parameters measured were observed during the study in cows fed diets supplemented with UMMB. It can be concluded that nitrogen supplied through UMMB had no effects on production performances of dairy cows in this study.