¡¾ABSTRACT¡¿The present study aimed to dissect the genetic basis of heterosis for grain yield and its components in maize (Zea mays L.). Quantitative trait loci (QTL) and heterotic loci (HL) were analyzed using a set of 203 single segment substitution lines (SSSLs) and its testcross population in three environments. Forty-one QTL were identified as responsible for grain yield, ear length, ear diameter, row number, kernel number per row, and 100-kernel weight in the SSSLs population, and 17 QTL were conserved across the three environments. In the heterosis analysis, 36 HL were identified for grain yield and five yield-related traits in the test population in the three environments. Among the HL, only six (16.7 %) for ear length, kernel number per row, 100-kernel weight, and grain yield were consistent with the results of QTL mapping. In addition, 16.7 % of the heterotic loci showed a dominant effect and 83.3 % showed an over-dominant effect. The results implied that dominance and over-dominance were two important components of heterosis in maize grain yield and yield-related traits in the present testcross population.