To evaluate the effect of cover crops, tillage systems and nitrogen (N) application rates on yield of forage sorghum (cv. KFs3), a factorial–spilt plot arrangement based on randomized complete block design with four replications was carried out at the Research Farms College of Agriculture and Natural Resources, University of Tehran, Karaj, during the growing seasons of years 2005 and 2006. Combinations of tillage systems, namely: either reduced (Disc) or conventional (Moldboard Plow+Disc) and N rates (0, 75 and 150 Kg.ha-1) were assigned to main plots, while winter cover crops (rye, hairy vetch and fallow or no cover crop) allocated to subplots. In either of the years, the tillage system did not affect the yield quantity and quality of forage sorghum, but significant differences were observed for N rates and cover crop treatments in terms of forage sorghum yield. Forage yields increased with increasing N rates, and the maximum yields were obtained with the highest N rates per hectare. There were significant differences observed between cover crop treatments as compared to check, but no significant differences between rye and vetch cover crops were recorded. Combined analysis showed significant differences for N rates and cover crop treatments in such qualitative attributes as digestive dry matter, soluble carbohydrates, crude proteins and ash. The results showed that using cover crops with 150 Kg of N ha-1 accompanied by reduced tillage system are advisable for forage sorghum production in Karaj region.