Technical Abstract: The GW2 gene on rice chromosome 2 controls kernel width and weight and has two copies in maize. In this study, we investigated the relationship, evolutionary fate and putative function of the two maize genes, ZmGW2-CHR4 and ZmGW2-CHR5. The two genes are located on duplicated maize chromosomal regions that show orthologous relationships with the rice region containing GW2. ZmGW2-CHR5 is more closely related to the sorghum counterpart than to ZmGW2-CHR4. Sequence comparison between the two genes in eight diverse maize inbred lines revealed that the functional protein domain is completely conserved, with no non-synonymous variations identified. This suggests a conserved function of both genes, which was further confirmed through linkage, association, and expression analyses. Linkage analysis showed that ZmGW2-CHR4 is located within a consistent quantitative trait locus (QTL) region for hundred kernel weight (HKW). Association analysis with a diverse panel of 121 maize inbred lines identified seven and five polymorphisms in ZmGW2-CHR4 and ZmGW2-CHR5, respectively, that associated significantly with at least one of the four yield-related traits, kernel length (KL), kernel width (KW), kernel thickness (KT) and HKW at P = 0.01 level. None of these polymorphisms are similar to the mutation causing phenotypic variation in rice. Expression levels of both genes vary over ear and kernel developmental stages, and the expression level of ZmGW2-CHR4 is significantly negatively correlated with KW. Collectively, these results show that the two genes represent chromosomal duplicated genes in the maize genome, both of which retain a function controlling some of the phenotypic variation for kernel size and weight in maize, as does their counterpart in rice, but the polymorphisms and thus, possible mechanisms causing phenotypic variations are different between the two species as well as the two duplicated maize genes.