This study evaluated the effects of dietary supplementation with brown macroalgae (Ascophyllum nodosum) at two inclusion levels (0.6% and 1.0%) on mineral digestibility, serum mineral concentrations, and femoral bone characteristics in piglets. A total of 210 piglets were randomly assigned to control (0%) or supplemented diets (0.6% or 1% macroalgae) from day 18 to day 64. Supplementation at the 1.0% level significantly improved digestibility and serum concentrations of essential minerals including calcium, phosphorus, magnesium, copper, and iron. Meanwhile, the 0.6% supplementation led to greater improvements in femoral bone mechanical properties, such as fracture load, elastic work, and work to fracture, as well as in material properties, including fracture and yield stress. These findings indicate that moderate supplementation with A. nodosum (0.6%) is most effective in optimising bone mechanical strength, and may represent a practical dietary strategy for improving skeletal development in fast-growing piglets.