Abstract: In a diallel cross rice involving five varieties (Dailamani, Sange-tarom, Hasani, Shastak-Mohammadi and Daei-shastak), combining ability and gene action for yield and yield-related traits were estimated. The study indicated that both general and specific combining ability effects were significant and important for the more traits, except for primary branching of panicles and paddy width traits. This indicates the role of additive and non-additive gene effects in inheritance of the traits. Variances due to GCA were greater than those due to SCA for plant height, flag leaf width, primary and secondary branching of panicles and filled grain per panicle traits, suggesting the role of additive gene effects were predominant in inheritance of the traits. These characters have high heritability and selection for them may well succeed. But, low heritability of tiller number, flag leaf length, days to maturity, panicle length, paddy length and width, 1000-grain weight and grain yield characters, were because of a high amount of non-additive variance in the genetic variance. Thus these characters were important for production of hybrid variety and exploitation of heterosis. The GCA effects of each parent for these traits showed that the Shastak-Mohammadi and Daei-shastak are good general combiner for days to maturity and grain yield, respectively.