Abstract The effect of caponization on the level of testosterone, biochemical bone markers as well as on the geometrical, densitometrical, structural, mechanical and microstructural characteristics of the tibia of capons was the subject of this study. The study was conducted on 80 hybrids obtained from the crossing of Rhode Island Red (R-11) hens and meat roosters (Ross 308). Cockerels were surgically castrated at 8 week of age and then fattened until the 24th week of life. The results indicated that the serum testosterone (P<0.01), osteocalcin (P<0.05), and osteoprotegerin (OPG) (P<0.05) concentration were significantly lower, while the serum receptor activator of nuclear factor-kappa B ligand (RANKL) (P<0.01), RANKL/OPG ratio (P<0.05) and alkaline phosphatase concentrations (P<0.05) were significantly higher in capons. The tibia weight, the relative tibia weight, and the cross-sectional area of tibia were significantly higher (P<0.05) in cockerels, while capons had higher (P<0.05) body weight and transversal external diameter of tibia. Moreover, the bone ash, calcium and phosphorus content, bone mineral density and bone mineral content, and also yield load, ultimate load, work to fracture, as well as Young’s modulus, bending moment, yield stress and ultimate stress were significantly lower (P<0.05) in capons. Caponization also caused a significant reduction in the percentage volume of bone (P<0.05) in the proximal epiphyses of the tibia, as well as changes in its microarchitecture (P<0.05) (fewer trabeculae and connections between trabeculae, thicker trabeculae and larger spaces between trabeculae). Concluding, caponization disrupts the homeostasis and microstructure of the tibia, and this results in a decrease in the mechanical strength of the tibia, making it more susceptible to deformation.