Abstract: Experiment of 8×8 diallel analysis was conducted on Upland cotton (Gossypium hirsutum L.) in the Faculty of Agriculture, Gomal University, D.I.Khan, Pakistan during copping season 1997-99. Sowing was managed both on Flat land and Ridges to differentiate the estimation of combining ability analysis in the inheritance of some important yield components viz., Seed Index, Lint %age, Lint Index and Staple length by Griffing’s Method- II, Model-1 in F1 generation. The mean squares for General Combining Ability (GCA), Specific Combining Ability (SCA) and reciprocals effects of both flat land and ridges plantation were observed to be highly significant for the characters mentioned. The estimates of component of variance clarified that the variance due to SCA was much higher in magnitude and more imperative than GCA for all the traits mentioned above except for lint index in flat land but the SCA was quite higher in style of ridges for all the parameters. This type of variance percentage surly indicated the significant role of non additive type of gene action with (dominance or epistatic effects) in the inheritance of these traits, though additive type of gene action was reflected in case of Lint index because of its higher GCA (Flate Land).