As a potent inhibitor of muscle growth, myostatin (MSTN) negatively regulates skeletal muscle mass. Since the discovery of double-muscled phenotype in MSTN knockout mice, MSTN have been considered as a potential genetic marker to improve meat production in livestock because MSTN mutant cattle, pigs and sheep showed double-muscled phenotype as well. Recently, our group demonstrated the anti-myogenic function of MSTN in avian species by generating MSTN mutant quail, further supporting MSTN as a potential genetic marker for increased meat production of poultry species. However, effects of MSTN mutation on other functional traits important in broiler and layer industries still needed to be investigated. Therefore, we investigated feed efficiency, fat accretion, and egg production in MSTN mutant quail. First, weight gain (WG) and feed intake (FI) were measured at 10-day intervals from post-hatching day (D) 10 to 40 to calculate feed conversion ratio (FCR), a major indicator of feed efficiency. Subsequently, leg and abdominal fat accretion in quail were analyzed at 8 weeks of age. Significantly higher WG from all time periods, but similar FI from D 30 to 40 in mutants compared to wild-type (WT) quail, resulted in significantly lower overall FCR in mutants, indicating improved feed efficiency by MSTN mutation in quail. In addition, significantly lower percentages of leg and abdominal fats in mutants compared to WT might partially contribute to improved feed efficiency in MSTN mutant quail by distributing energy intake toward muscle growth and away from fat deposition. Next, ages at first egg and weight and number of laid eggs for 20 days from 3-month-old mutant and WT quail were analyzed. Although egg weights were significantly heavier in mutants compared to WT, ages at first egg and total number of eggs during the active laying period were significantly late and low, respectively, in mutants. Taken together, future usage of MSTN as a genetic marker will be more practical in selection of superior lines of broilers for better meat production and feed efficiency, but not in layers for overall egg production.