<p>The present investigation was aimed to determine the general combining ability of the parental lines and specific combining ability of the hybrids respectively and also heterotic effect of F₁ hybrids for some agro-economical traits in upland cotton. Five parent genotypes viz. NIAB-78, Chandi-95, Haridost, CRIS-134 and Shahbaz were used to generate ten F₁ hybrids through diallel mating design. The seeds of F₁ hybrids along with their parents were sown in Randomized Complete Block Design (RCBD) in three replications during 2009-10. All the traits showed highly significant variation and GCA and SCA variances were also significant for all the parameters studied. Among the parents, NIAB-78, Haridost and CRIS-134 were best general combiners for plant height, sympodial branches per plant, bolls per plant, boll weight, seed cotton yield per plant, GOT% and seed index. Cross NIAB-78×Chandi-95 was best specific combiner for plant height and bolls per plant and CRIS-134×Haridost for sympodial branches per plant. However, the hybrid Chandi-95×CRIS-134 proved best specific combiner for seed cotton yield per plant and GOT%, while NIAB-78×CRIS-134 gave maximum SCA effects for seed index.</p>