Field experiment was conducted during winter seasons of 1993–94 and 1994–95 to study the effect of irrigation and nitrogen levels on periodical plant height, number of primary branches and dry matter accumulation of Brassica species. Pooled data of two years showed that Brassica species RH-30, NPC-2 and HC-9001 recorded 178.5,238.3 and 229.2 cm plant height; 5.5, 10.3 and 10.1 number of primary branches and 45.92, 48.62 and 47.68 g dry matter per plant at harvest, respectively. Irrigation treatment I 2 (ID/CPE ratio of 0.5) had significantly more plant height, number of primary branches and dry rtiatter accumulation over I 0 (no post-sowing irrigation) and 11 (ID/CPE ratio of 0.25).Plant height, number of primary branches and dry matter accumulation per plant at harvest in I 2 treatment were 6.43 and 11.13, 11.31 and 16.15, and 17.42 and 20.98 per cent. over I 1 and I 0 irrigation treatments, respectively. Plant height and dry matter accumulation increased significantly with successive increase in N levels upto 90 kg ha −1. The number of primary branches increased significantly upto 60 kg ha −1.