A study was under taken during kharif season of 2016 at College of Agriculture, Bheemarayanagudi and UAS, GKVK, Bengaluru to estimate the combining ability and investigate gene action involved in inheritance of yield and its components traits of maize inbreds through 20×20 full diallel cross analysis. 380 SCHs synthesized through full diallel mating design were evaluated in simple lattice square lattice design at two locations. Analysis of variance revealed significant differences among the hybrids, parents vs. hybrids and straight crosses for all the characters and among the parents for all the characters except ASI, ear circumference and shelling %. Significant differences were also recorded in reciprocal crosses for all the characters except ear circumference and shelling %. Significant GCA variance for grain yield revealed the role of additive components of genetic variance. SCA variance was also highly significant for all characters except ear circumference and test weight indicating the importance of both additive and non additive components of genetic variance. However, there was predominance of additive gene action recorded for all the characters. GCA: SCA variance ratio was less than unity for all the traits, suggesting the predominance of non-additive gene action. Inbreds MAI 283 and VL 109252 were identified as good general combiners as they registered significant gca effects in positive direction for grain yield and its component traits. Straight cross MAI-283×KDMI-16 and reciprocal cross M 04×KDMI 16 registered highest significant sca effects in positive direction for grain yield along with high and significant sca effects in negative direction for ASI.