Plant growth regulators (PGR's) allow for manipulation of physiological processes in cotton leading to altered growth and development. Field experiment were conducted at Agricultural Research Station, Dharwad, Karnataka during 2010-11 to determine the effect of PGR's on morpho-physiological traits and yield attributes in Bt cotton hybrids (MRC-6311) to foliar application of Mepiquat chloride (25, 37.5 and 50 ppm), chlormequat chloride (375 and 500 ppm) at 45 and 90 DAS and NAA (20 ppm) at 90 DAS. Application of growth retardants at earlier stages (45 DAS) severely affected the plant growth and seed cotton yield as compared to any other treatments. NAA (20 ppm) recorded maximum plant height and more number of main stem nodes as compared to untreated control. Foliar application of NAA (20 ppm) at 120 DAS recorded higher rate of photosynthesis, stomatal conductance and transpiration whereas high total chlorophyll content was observed in growth retardant treatments as compared to control. The growth promoter NAA (20 ppm) recorded significantly higher number of bolls per plant, boll weight and seed cotton yield followed by MC (50 ppm) sprayed at 90 DAS over untreated control.