Six populations (P1, P2, F1, F2, BC1 and BC2) of three bread wheat(Triticum aestivum L.) crosses, mamely Gemmeiza 9 x Mayon"S"//Crow"S"/Vee"S" (cross I), Attila/Sids 1 x Sakha 94 (cross II) and Mayon "S"//Crow "S"/Vee"S" x Attila /Sids 1 (cross III) were used to estimate genetic parameters for grain yield/plant and certain related characters under two nitrogen fertilizer levels; (40 Kg N/Fed [low level] and 75 Kg N/Fed (recommended level]). Results revealed that heterosis values were positive and significant relative to better-parent in the three crosses under the two nitrogen levels for most of the studied characters. Meanwhile, heterosis values were negative and significant for number of kernels/spike in the first and the third crosses under low level of nitrogen N1, and the third cross under recommended level N2 and for kernel weight in the second cross under N1. In the second and third crosses under N2, positive and significant inbreeding depression values were recorded for all studied characters in the first cross except for kernels/spike under both N1 and N2, for kernels/spike in the second cross under both N1 and N2, for spikes/plant and grain yield in the third cross under N1 and N2, whereas negative significant values were obtained for kernels/spike in the third cross and for kernel weight in the second and third ones under both levels of nitrogen. Over-dominance above the higher parent was detected for spikes/plant and grain yield in all crosses under the two levels of nitrogen, for kernels/spike in the first cross under N2 as well as in the second cross under N1 and N2 and for kernel weight in the first cross under two levels. The other types of dominance were also studied. Scaling tests (A, B, C and D) indicated the presence of non-allelic gene interactions for all studied characters in all crosses under both levels of nitrogen. Additive genetic variance was highly significant for all traits in the three crosses under N1 and N2. Dominance variance was significant for all characters in all crosses, except for kernels/spike and kernel weight in the second cross under N1 and for all characters except for kernels/spike in the first cross, for kernel weight in the second cross and for all characters except for kernel weight in the third one under N2. Epistasis effects were present for most studied traits in the three crosses under both levels of nitrogen. F2 deviations (E1) was significant for kernel weight in all crosses, spikes/plant in the second and third crosses and grain yield in the second cross under N1 as well as for spikes/plant and kernel weight in all crosses and grain yield in the first and second crosses under N2. Back-cross deviations (E2) were significant for kernel/spike and grain yield in the first cross, for kernel weight in the second cross and for all characters in the third cross under N1 as well as for spikes/plant and grain yield in the first cross, for kernels/spike and kernels weight in the second cross and for all characters except for spikes/plant in the third cross under N2. Broad sense heritability estimates were relatively high under both N1 and N2. Selection in segregating generation could be effective to produce lines that have high yielding ability under low level of nitrogen fertilizer (40 kg N/fed).