A crossbreeding experiment was carried out using two selected lines of Japanese quail (the brown line and the white line; lines were established for egg and meat production). A total of 2450 crossbred birds of quail produced from four mating groups (two groups for pure birds and other two groups for cross lines) among three hatches were used in the present study to estimate direct heterosis, direct additive, and maternal effects on the following traits: growth traits: body weight at 0, 2, 4, and 6 weeks of age  and average daily gain at different growth intervals (ADG_0-2, ADG_2-4, ADG_4-6, and ADG_0-6)and  carcass traits: slaughter weight (SW), meat (M%), bone (B%), giblets (G%), and dressing percentages (D%). Results showed that crossing sires of BB with WW dams had the highest body weights and body weight gains recorded from hatch to 6 weeks of age, followed by reciprocal crossing between sires of WW with BB dams. Except for BW4 and body weight gains calculated between different growths periods studied, most body weights recorded at different ages showed a highly significant positive direct heterosis effect. Crossing sires of BB with WW dams had the highest carcass performance, followed by reciprocal crossing between sires of WW with BB dams. The majority of carcass traits studied showed a positive direct heterosis effect, with the exception of M% and G%, where direct heterosis was non-significant.