Abstract: Maize is a major cereal for human nutrition in Ethiopia. For communities that rely heavily on maize as the main staple, development of maize cultivars with enhanced levels of two essential amino acids such as lysine and tryptophan are a must. The objectives of the study were to find out the combining ability, the nature and magnitude of gene action and heterosis of quality protein maize inbred lines. Six inbred lines and two testers were crossed to produce 12 F1 hybrids. Twelve F1 hybrids and two standard checks viz., BHQP542 and a normal maize hybrid, Jibat, were evaluated in a randomized complete block design with two replications in 2011 at Adet. Although it was a one season trial, LN1, LN2 and LN5 were good general combiners for grain yield and yield component characters and can be used for development of hybrids. Hybrid HN7 (81.1%), HN8 (107.3%) and HN11 (88.3%) had higher magnitude of heterosis over the quality protein maize check but these hybrids were not superior over the normal maize check. From this result hybrid HN7, HN8 and HN11 can be exploited for future use and additional effort is required for the development of competent quality protein maize.