Field experiment was conducted during rabi 2013-14 and 2014-15 to study the thermal requirement for Indian mustard at research farm, College of Agriculture, Hisar,Haryana (latitude 290 10’ N and longitude 750 36’ E Latitude). The experiment was laid out in split plot design with three replications consisted four dates of sowing (Oct15th&25th and Nov5th& 15th) as main plots and five nitrogen levels(0 (Control), 40, 60, 80 and 100 kg N ha-1) as sub plots treatments. Results revealed that duration of phenological stages and thermal unit during days to 50 % flowering to maturity increased with successive delay in sowing. October 15 sowing crop produced significantly higher total dry matter accumulation, more number of siliquae, higher seed yield, and biological yield as compared to October 25, November 5 and November 15. Among the doses of nitrogen, 100 kg Nha-1 exhibited significantly higher total dry matter accumulation, heat use efficiency, more number of siliquae plant-1, higher 1000 seed weight , seed yield and biological yield followed by 80, 60, 40 and 0 kg N.