Abstract: A study was carried out at Songa research station of Rwanda Agricultural Research Institute (ISAR) in the Southern Province to evaluate the effect of supplementation with 3 levels of Leucaena diversifolia Leaf Meal (LDLM) on milk yield of crossbred dairy cows. Sixteen Jersey x Ankole first and second lactation cows with average body weights of 312 kg and within 30 Day in Milk (DIM) were allocated to four treatments each having four cows in a completely randomized design. As a basal ration, the cows were grazed in paddocks with a mixture of natural grasses mainly Hyparrhenia rufa, Themeda triandra, Panicum maximum, Brachiaria humidicola and Cynodon dactylon for 8 h day^-1 and later were offered 4 kg of chopped Pennisetum purpureum each in the evening after milking. Treatment diets were 0.0 (T₁), 1.48 (T₂), 2.21 (T₃) and 2.80 (T₄) kg of Dry Matter (DM) of LDLM equivalent to 0, 10, 20 and 30% of LDLM, respectively. All cows received equal amounts of the dietary treatments twice a day at 07:00 and 16:00 h. Other components of supplementary rations were rice bran (1.74 kg DM) and minerals which were in form of blocks. Inclusion of LDLM in the rations of dairy cows gave a significant (p<0.001) increase in milk yield. Cows on T₃ diet gave a significantly (p<0.001) higher milk yield (8.44 kg/cow/day) and cows on T₁ diet gave the lowest yield (6.01 kg per cow per day). Cows on T₂ and T₄ diet had similar (p>0.05) milk yield of 7.32 and 7.97 kg/cow/day, respectively. In conclusion, it is suggestive that inclusion of 30% LDLM in the ration of lactating crossbred cows was the optimal supplementation level.