Heterotic effects wee studied over mid parent and better parent values for seed yield and its components in 21 crosses derived from a diallel mating design involving 7 diverse parents of lentil. Hybrids were evaluated alongwith their parents in the experimental field of Agricultural Research Station, Ummedganj, Kota, Rajasthan. The heterosis for seed yield/plant ranged from -20.74 to 42.61 % over better parent. Considering overall performance, hybrids viz., RL3 x KLB 339, IPL 313 x RKL 1001 and RL 3 x RKL 11 were the best for seed yield exhibited high heterosis over better parent, good per se performance and significant sca effect along with one good general combiner indicating non-additive gene action played major role for expression of high heterosis for seed yield. These hybrids are, therefore, suggested to be utilized for developing high yielding lentil cultivars through conventional breeding methods such as biparental mating, diallel selective mating and multiple crossing followed by recombination