In this study, change in proximate composition in forage sorghum cultivars as influenced by nitrogen (N) fertilization and seed rate harvested at different growth stages was planned through field experiments during consecutive years. Three forage sorghum cultivars viz., JS-2002, JS-263 and Chakwal sorghum were sown under three N levels (0, 60 and 120 kg ha-1) by using three seed rates i.e. 75, 100 and 125 kg ha-1. Results showed that all individual effect of treatments had a variable influence on quality of sorghum cultivars. JS[1]2002 had higher crude protein content (CP), crude protein yield (CPY), crude fiber (CF), crude fiber yield (CFY), ether extractable fats (EE), total ash content (TA) and organic matter (OM) whilst JS-263 produced greater nitrogen free extract (NFE) than other cultivars. Increasing N rates (0 to 120 kg ha-1) raised all above mention bio-chemical attributes but not NFE. Similarly, increased seed rate enhanced accumulation of CP, CF, EE, TA, CPY and CFY while caused reduction of OM and NFE. Genotypic variations may have influenced the accumulations of these traits however, differences were not significant. In conclusion, sorghum cultivar JS-2002 seeded at 75 kg ha-1 with 120 kg N ha-1 application produced better quality forage under sub-tropical conditions