A two-year study was conducted on maize (Zea mays L.) at the University of Ilorin Teaching and Research Farm Ilorin, Nigeria, during 2005 and 2006 growing seasons. The objective was to investigate correlation between grain yield and other agronomic parameters using 10 open-pollinated maize varieties and their 45 F1 hybrids in a half diallel. Positive and significant phenotypic and genotypic correlations were found for days to 50% tasselling with plant and ear height, and grain yield with plant height, number of grains ear-1 and ear weight. Positive and significant environmental correlation was also recorded for grain yield with plant and ear height, and ear weight. The path analysis revealed that, days to 50% silking, ear weight and number of grains ear-1 had the highest direct effect on grain yield, while number of grains ear-1 had the highest moderate indirect negative effects on grain yield. Days to flowering, plant and ear height, number of grains ear-1 and ear weight could be the important selection criteria in improving open pollinated maize varieties and hybrids for high grain yield.