INHERITANCE of yield and yield contributing characters were investigated using generation mean analysis, utilizing the means of six populations in parents, F1, F2 and backcross generations of three crosses of bread wheat using six parameters model under favorable and heat stress conditions. This study was carried out during the three successive seasons of 2009/2010, 2010/2011 and 2011/2012 at the Experimental Farm of Faculty of Agriculture, Sohag University, Egypt. The objective of this study was to determine nature of gene action controlling yield and its components. Additive (d) and additive x additive were highly significant and positive for most traits in all the three crosses under favorable sown and heat stress, suggesting the possibility of obtaining further improvements of these traits using a pedigree selection method. Dominance and dominance x dominance gene actions were also found, though the significance and direction was specific for each environment and genotypic cross, indicating the importance of dominance gene effects. Heritability estimates in narrow sense in F2 were relatively high to moderate more than 34.26% and 42.22% under favorable and heat stress, respectively. The promising crosses were the first cross (Giza164 x Qimma 4) and third cross (Gemmeiza 9 x Johara14), were found to high in magnitude which had high genetic advance associated with high heritability and would be interest in breeding programs for heat tolerance.