A set of thirty-five genotype of Indian mustard (Brassica juncea (L.) Czern & Coss.) were evaluated to study genetic variability and interrelationship among physio-morphological characters under heat stress. High values of GCV coupled with heritability were observed for LAI (30 DAS), LAI (60 DAS), SLW (60 DAS), CGR, secondary branches/plant and seed yield/plant suggesting that additive gene action might play major role in the expression of these characters and selection would be rewarding in further improvement of these characters. High heritability estimates coupled with high genetic advance was observed for LAI (30 DAS), LAI (60 DAS), SLW (60 DAS), secondary branches/plant whereas high heritability with moderate genetic advance was observed for seed yield/plant. Significant correlations among most of the physio-agro-morphological traits were found during different growth stages. Seed yield/plant was exhibited positive and significant correlation with secondary branches/plant, harvest Index, seeds/siliqua, chlorophyll content (60DAS) and 1000 seed weight. Seed yield/plant showed positive and highly significant correlation with days to physiological maturity (r=0.6276**). which could be considered as one of the important selection criteria in the improvement of seed yield under heat stress situation.