Heterosis and combining ability of protein content in rice were studied by using 5x5 half diallel cross. Five local and exotic rice varieties with different protein content % were used. Parental and their hybrid varieties were arranged in a randomized complete block design with three replication .Protein content % was estimated. Analysis of variance showed highly significant differences among genotypes, highly significant and positive estimates of heterosis were recorded for protein content % when it measured as a deviation from mid-parent in three crosses, on the other hand and highly significant and positive estimated of heterosis was recorded (Giza 179x IR 64) rice cross when it was measured highly significant a deviation from the better parent. Further the general to specific combining ability ratio was (1.16) suggested the influence of both additive and non additive genetic variances in the inheritance of such character. Only BG304 variety rice shows highly significant and positive estimate of general combining ability (GCA) effects with value 0.821, proving that this parent appeared to be good combiner in rice crosses for improving this trait. The best crosses were Hexi 12x IR 64, Giza 179x IR 64 and Milyang 97x IR 64. These crosses gave 0.562, 0.630 and 0.492, specific combining ability (SCA) estimates, respectively .The crosses which gave highly significant and positive estimates could be used as a donor for increase this trait. Broad narrow sense values were high for this character; the additive gene action plays an important role in the inheritance of this character,although genetic variation appeared to be influenced predominantly by genes with additive and dominance effect.