The current study was carried out to investigate the consequences of mannan-oligosaccharides (MOS), a prebiotic, as feed supplement on biochemical parameters of Japanese quail breeders (Coturnix coturnix japonica). Twelve-week-old, 960 birds, belonging to 4 close-bred flocks (CBF), were randomly selected and divided into 4 treatment groups with 3 replicates according to pattern (4 strains × 4 treatment groups × 3 replicates). Birds were fed corn-based basal diet or the same diet supplemented with 0.25, 0.50, and 1.0% MOS for 15 wk. After termination of the experimental trial, samples of blood were taken from randomly selected 3 birds/replicate (1♂ and 2♀) and processed for serologic analysis. The statistical analysis was performed by applying 2-way analysis of variance. The serum concentrations of total proteins, globulin, high-density lipoprotein, and tri-iodothyronine (T3) of Japanese quail breeders were significantly (P < 0.05) higher in MOS-supplemented groups than that of control group; however, triglycerides were decreased significantly (P < 0.05) by MOS supplementation in female birds. Estrogen level in male birds was significantly (P < 0.05) different; however, non-significant differences were recorded in thyroxine (T4), progesterone, alanine aminotransferase, aspartate aminotransferase, glucose, albumin, cholesterol, and low-density lipoprotein concentrations in all feeding groups. The significant differences in biochemical parameters by feeding MOS-supplemented diets strengthened our hypothesis that the use of MOS may positively affect the health of Japanese quail breeders.