Knowledge of gene action enables breeders to design effective breeding strategies for the improvement of genotypes. Half diallel cross among limmu coffee (Coffea arabica L.) genotypes comprising 5 parents, 10F₁ hybrids, and two checks carried out at agricultural research (Jimma, Agaro, and Gera centers) for the objective to determine nature of gene action and combining ability effects of diallel genotypes for yield and its components in 2017/18. Randomized complete block design (RCBD) with three replications used. Combined analysis of variance revealed significant (P<0.05) variation among 17 and 15 diallel genotypes for 24 traits indicating the presence of genetic variability for these traits. The mean square due to GCA and SCA was significant for 13 traits including yield, which implies both additive and non-additive gene actions involved for the expression of these traits. Additive gene action contributed a lot to nine traits including all fruit and bean traits than non-additive gene actions. However, non-additive gene action more contributed than additive gene action for 11 traits including yield (77.57%). GCA effect estimate showed the best general combiners were parent P₄ (L55/01) for yield, P₁ (L20/03) for all fruit and bean characters, and parent P₂ (L67/01) for three growth, leaf, and fruit traits. Based on the SCA effect, the best crosses were P₄×P₅ followed P₁×P₅ and P₂×P₅ for yield, P₂×P₄, and P₃×P₄ for six and five different traits, respectively. These hybrids could be used in variety development after testing for other desirable traits.