Abstract: Six upland cotton (G. hirsutum L.) varieties were crossed in all possible combinations. The parents and F₁ were sown in a replicated experiment. Hayman’s diallel cross analysis was employed to investigate the nature of gene action involved in the inheritance of number of sympodial branches per plant, number of bolls per plant, boll weight, yield, ginning out turn %, staple length, fiber fineness and fiber strength. The diallel analysis revealed that all the characters were polygenically inherited and exhibited partial dominance with additive gene action. The estimation of component of variation for these characters suggested that the (D) additive component was significant in all the traits under study and was lower than dominant components (H₁ and H₂) of variation except for number of sympodial branches per plant, number of bolls per plant and seed cotton yield per plant, where the dominant components were higher in magnitude than additive. The positive estimate of F indicated that dominant genes were in excess than recessive genes in the parents for all the traits except for ginning out turn percentage and fiber fineness. The ratio of H₂/4H₁ indicated largely asymmetry of positive and negative genes in parents for number of bolls per plant, seed cotton yield, staple length, fiber fineness and fiber strength, and symmetrical distribution of positive and negative genes in the parents was observed for number of sympodial branches per plant, boll weight and ginning out turn percentage. The h² value for number of number of sympodial branches per plant, number of bolls per plant, boll weight, seed cotton yield per plant, ginning out turn, staple length, fiber fineness, and fiber strength was positive and significant which indicated that hetrotic breeding was rewarding for these traits. The correlation between W_r + V_r and Y_i indicated that dominant genes are mainly responsible for the expression of all traits. Mass selection will be an effective method for improving the boll weight and reciprocal recurrent selection method will be helpful for improving the sympodial branches per plant, number of bolls per plant, seed cotton yield, fiber fineness and fiber strength. The full sib or half sib family selection, pedigree and progeny test would probably be necessary to achieve the genetic progress for GOT% and staple length.