An experiment was conducted during winter seasons of 2005-06 and 2006-07 to study the nature and magnitude of gene effects involved in the genetic control of seed yield and yield attributing traits in Indian mustard [Brassica juncea (L.) Czern and Coss.] through generation mean analysis. Two crosses namely; RH 0115 x EC 126745 and RH 0120 x EC 126745 were grown in a randomized block design under normal and late sown conditions. In six parameter model additive gene effects were significant for days to maturity, number of primary and secondary branches per plant, number of seeds per siliqua and oil content. Both additive and non-additive gene effects were found to be significant for main raceme length, number of siliquae on main raceme, seed yield per plant and 1000-seed weight. Thus on the basis of above study it is advocated that the breeding methods which exploit both the components of genetic variation may be useful for further genetic amelioration. For the improvement of seed yield and its component characters; reciprocal recurrent selection or diallel selective mating would be helpful.