Field experiment were conducted during kharif season of 2013-14 and 2014 -15 at Agriculture Research Station,Dharwad to study the “Physiological studies in Cotton hybrids G.hirsutum L. differing in morpho-physiological traits”. Theexperiment consisted of thirty hirsutum x hirsutum cotton hybrids and their twenty three parents laid out in randomized blockdesign with three replications on medium black soil and worked out heterosis. Hybrids and their heterosis were assessed foryield, Number of bolls, boll weight, total dry weight, leaf area, plant height and specific leaf weight. Seed cotton yield differedsignificant among the hybrids. It ranged from 1178.2 kg ha-1 to 2184.9 kg ha-1. Among the hybrids, RGR x SG-4 recordedhighest seed cotton yield (2184.9 Kg ha-1). Higher seed cotton yield was mainly attributed to its close association with totaldry matter (0.727), leaf area (0.720.) and medium plant height (0.130) and specific leaf weight (0.509). Heterosis for seedcotton yield was maximum in RGR x SG-2 (72.3%), but total dry matter, leaf area, plant height and specific leaf weight itwas recorded more in RGR x RGR-4 (44.5 %), RGR x SG-2 (1047.6%), SG x RGR-5 (35.3 %) and SG x RGR-2 (152.9 %).These traits possibly increase the number of bolls per plant (32.1) and boll weight (5.99). There by it increase seed cottonyield in RGR x SG-4.