Data of the present study were obtained on a total of 2502 birds of purebred (1300) and crossbred (1202) birds of two differently selected Japanese quail lines (paternal and maternal), as well as their reciprocal crosses. The studied traits were weekly body weight from hatch up to 6th week of age, body weight (BWSM) and age at sexual maturity (ASM) of females, egg number for the first 50 days of production (EN50) and degree of sexual dimorphism for body weight (DSD) weekly from hatch to 6th week of age. The crossbreeding effects (heterosis, direct additive, maternal additive) were estimated for all traits. Fixed effects (line, sex and hatch) and their possible interactions were included in the models to analyze the studied traits. Line differences were significant for all traits. Paternal line showed expected significant (P<0.05) superiority over the rest of the genetic groups for body weight traits. Both crossbreds showed significantly (P<0.05) better performance in ASM, EN50 and DSD than their purebred parents. Degree of sexual dimorphism (DSD) for body weight was significant (P<0.05) at later ages at 5th and 6th weeks but not apparent earlier in the whole experiment. Both sex and hatch significantly (P<0.05) affected body weight traits, except the effect of sex on hatch weight. Hatch effect was significant (P<0.05) on BWSM, ASM and EN50. Direct heterosis was almost significant (P<0.05) for all traits, except for WH though generally negative for body weight traits, while it was positive and significant for EN50 and most of DSD traits. Direct additive and maternal additive effects were significant (P<0.05) for most traits, except for WH, ASM and EN50, where only direct addtive effect estimates were significant. DSD traits showed inconsistent effects and trends for both direct and maternal additive effects. Impact of additive rather than maternal effects were clear in most traits. Generally, it could be concluded that crossbreeding between one paternal line with another maternal line had negative heterotic effects on body