The present study was done at the Experimental Farm of Sakha Agricultural Research Station, Kafr El-Sheikh, Egypt, during 2016 and 2017 seasons to study combining ability, gene action and heterosis for grain yield and some agronomic traits in some lines to be utilized in hybrid rice development. The experiment comprised 30 crosses derived from six varieties/lines namely; Dular, Jip 5, O2428, Nekken 1, Giza 181 and Giza182. A complete diallel cross set was done among these six rice parents including reciprocals. General combining ability and specific combining ability were found to be highly significant for all studied traits. This indicated the importance of both additive and non-additive genetic variances in determining inheritance of grain yield and related traits. While, highly significant reciprocal effects were detected for most studied traits indicating presence of the maternal effects in controlling of studied traits except panicle length and panicle weight for these rice crosses. The ratio of GCA/SCA was more than unity for all studied traits, indicated the preponderance of additive gene effects in the expression of these traits. Rice varieties; Dular, O2428 and Nekken 1 showed highly spikelets fertility (> 70%) when they crossed with both japonica and indica cultivars indicated that these lines can be identified as wide compatible genotypes. Moreover, the three crosses of Nekken 1 X Giza 182, Giza 181 X Giza 182 and Nekken 1 X Giza 181 were the best specific combiner for grain yield.