Combining ability analysis using top cross method was performed in high quality protein maize (QPM) inbred lines for yield and yield contributing characters in order to assess the QPM inbred lines for general combining ability (gca) and to estimate mid parent and standard heterosis. The major interest was to seek out specific set of lines having maximum genetic distance that maximizes expression of heterosis in hybrid combination. The top cross, I14 x S superceded the checks in grain yield followed by the other crosses I6 x S, I4 x S, I3 x S, I18 x S and I7 x S. Significant positive gca effects for grain yield were revealed by the inbred I3, I4 and I6. Mid parent heterosis was observed to be 53.08% for grain yield in cross, I14 x S. The cross showed highest standard heterosis for grain yield (36.83%). The inbred line I7, I18 and I20 revealed negative significant gca effects for days to 50% silking which can be utilized for developing early maturing hybrids.