The experiments were carried out at Sakha Agriculture Research Station, Cotton Research Institute, Agriculture Research Center, Egypt. The aim of this investigation was to study heterosis and combining ability for the most important characters of cotton (seed cotton yield, lint yield, boll weight, seed index, lint percentage, lint index and hallo length). Ten cotton genotypes TNB, Karsheneski 2, G.45, G.89 x G.86, G.86, G.94, G. 93, CB.58, G.75 x Sea and Australian  12 were crossed in half diallel. These parents and their respective 45 F1 crosses were evaluated in a randomized complete blocks design. The results obtained could be summarized as follows:-Highly significant mean square values were obtained for genotypes, general combining ability and specific combining ability for all the studied characters. The best general combiner for all studied traits were parents G.94 and G.75 x sea. Also the best combination for most of studied characters were crosses G.45 x CB 58, TNB x Aus.12, Kar.2 x G.94, G45 x CB 58, G.94 x(G.75 x sea) and G.93 x (G.75 x sea). The first three principle components were significant and accounted about 90.3% of the total variability of all characters. Which having maximum Eigen value. Lint index followed by lint percentage, boll weight and lint yield were a primary source of variation in the first ax. The second ax was principally affected by seed cotton yield and hallo length. The ten parents in this study were grouped in different clusters and there were accordance between parental diversity and significant general and specific combining ability.