A half diallel cross among 5 inbred lines of maize was evaluated under  two different nitrogen rates  for  flowering  and vegetative characters i.e. anthesis date, silking date, Anthesis-Silking Interval (ASI), plant height,  ear  height, ear leaf area  and stem  diameter, to evaluate  the role of GCA  and  SCA  of  inbred  lines  in  hybrids  performance  under high  and  low  of  nitrogen  levels, and to  establish  the magnitude of heterosis as well  as  both  GCA  and  SCA  effects  and   their interaction with the nitrogen fertilization rates. Mean squares were  significant for all studied traits except, ear leaf area under normal nitrogen level. General and specific  combining  ability (GCA  and  SCA) mean squares were  significant  for all  studied  traits, except stem  diameter  under  normal  nitrogen  level at GCA and ear leaf area under normal nitrogen level at GCA and SCA. GCA/SCA  ratios  revealed  that  the  non-additive  gene  action  for  anthesis  date, silking date,  plant  height under  normal nitrogen, ASI, ear height, stem diameter under both nitrogen levels and ear leaf area under stress nitrogen level. While, the additive  gene  action was recorded for anthesis date, silking date and plant height under stress nitrogen level and ear leaf area under normal nitrogen level.  The  additive  gene  action was the most  expression under normal nitrogen  level. The  best  combiners  were  P₂ (Inb.95) and P₄ (Inb.204)  inbred  lines  for  most  of  studied  traits    under  normal  and  stress  nitrogen  levels. This  result  indicated  that  these  inbred  lines  could  be  considered  as  good  combiners  for  improving  these  traits. The best  crosses  for  anthesis and ASI  date  was P₂ (Inb.95) X P₅ (Inb.213), for silking date  was P₂ (Inb.95) X P₃ (Inb.144),  for plant height was P₃ (Inb.144) X P₅ (Inb.213), ear height was P₁ (Inb.84) X P₄ (Inb.204) and stem diameter was P₄ (Inb.204) X P₅ (Inb.213)  under  both  nitrogen  levels. These  crosses  could  be  selected  and  used  in  breeding  programs  for  improving  these  traits. Results showed significant heterosis for all studied traits.  The best crosses over both their mid-parents and better-parents for anthesis  date and silking date was P₂ (Inb.95) X P₃ (Inb.144) under both nitrogen levels for ASI date was P₂ (Inb.95) X P₅ (Inb.213), for ear height was P₁ (Inb.84) X P₄ (Inb.204),  for plant height was P₃ (Inb.144) X P₅ (Inb.213), for ear leaf area was P₁ (Inb.84) X P₃ (Inb.144) under stress nitrogen level and for stem diameter were P₂ (Inb.95) X P₅ (Inb.213), P₃ (Inb.144) X P₅ (Inb.213) and  P₄ (Inb.204) X P₅ (Inb.213).