Abstract: The influence of sowing dates carried out on 5 April, 20 April, 5 May and 20 May as well as nitrogen-fertilizer applied in 0, 50, 100 and 150 kg ha -1 dosages were studied on the growth, seed yield and seed swelling factor of isabgol (Plantago ovata). The best time for sowing of isabgol in this region was 5 May and the suitable amount of nitrogen was 100 kg ha -1. The stepwise multiple regression analysis verified that the seed yield among other characters studied showed a significant positive effect on seed swelling.