Twenty five new yellow inbred lines of maize were mated to two inbred lines(Sk11 and Sk2) as testers during 2014 season. The resulting 50 hybrids and the check hybrid SC168 were evaluated in three trials during 2015 season. The first for grain yield (t/ha) was conducted at Sakha and Sids research stations, the second and the third for late wilt and downy mildew resistance, each one was performed in two trials under two nitrogen levels(143 and 286 kg N/ha), respectively in two separate disease nurseries at Sakha Research Station. The first nursery under artificial soil inoculation by late wilt disease and the second nursery under artificial infection by downy mildew disease. The results were combined analysed across the two locations in the first trial and across two nitrogen levels in the second and third trials. Mean squares due to lines, testers and their interaction were significant for all traits, except for the interaction between lines x testers for late wilt resistance. The interactions lines, testers and lines x testers with locations were significant for grain yield, while their interactions with nitrogen levels were not significant for late wilt and downy mildew resistance. The non-additive gene effects were the most important component controlling the inheritance of all studied traits. The best inbred line for general combining ability effects was L6 for grain yield and downy mildew resistance and L10 for late wilt resistance. The best hybrid for specific combining ability effects was L22 x Sk2 for gain yield, L20 x Sk2 for late wilt resistance and L13 x Sk2 for downy mildew resistance. The hybrid L6 x Sk11 had high grain yield (>check) and high resistance to both late wilt and downy mildew. The 25 inbred lines were classified into the following two heterotic groups using HSGCA: for grain yield: group 1 (SK11): L9, L10, L11, L12, L15, L19, L22 and L23 and group 2 (SK2): L1, L2, L3, L5, L14, L16, L17, L21, L24 and L25 , for late wilt resistance: group 1 (SK11): L3, L15, L16, L19, L20, L21 and L25 and group 2 (SK2): L1, L4, L6, L7, L11, L12, L13 and L14. For downy mildew resistance: group 1 (SK11): L1, L2, L13, L15 and L21 and group 2 (SK2): L3, L4, L7, L12, L14, L17 and L25. These groups could be used in breeding programs for selecting the best parents in making crosses.