A one-way diallel cross among six common wheat genotypes were evaluated in F₁ at Etay EI-Baroud Agricultural Research Station during 2018/2019 and 2019/ 2020 seasons. These diallel F₁ crosses were made to determine heterosis and types of gene action for grain yield/plant and its attributes traits under different nitrogen rates. Highly significant and positive heterotic effects for 1000-kernel weight were detected in (P2×P3), (P2×P4), (P1×P5) and (P2×P6) at the three nitrogen rates. Meanwhile, the crosses (P1×P4), (P1×P6), (P4×P6) and (P5×P6) recorded positive and significant heterotic effects for 1000-kernel weight under normal (75 kg N/fed.) nitrogen rate. The grain yield/plant showed significant and negative heterotic effects relative to the better parent for most crosses at the three nitrogen rates except (P1×P2), which showed positive and significant heterotic effects. General combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant for all traits, and GCA/ SCA ratios were greater than unity for all studied traits at three nitrogen rates.The parental genotypes P1(Gemmeiza 12), P2 (Gemmeiza 9), P₃ (Giza 171), P4 (Line 1), P5 (Line 2), P6 (Line 3) appeared to be the best general combines for grain yield and some of its components in the three nitrogen rates. The cross combinations (P1×P2), (P2xP3) and (P2xP4), (P2xP5), (P2xP6), (P3xP5), (P4xP5), (P5xP6) were superior to their parental genotypes for heterosis relative to better parent, general and specific combining ability under three nitrogen rates.