This work explores novel biocomposite hydrogels fabricated using 40% (wt/vol) solution of whey protein isolate (WPI, from the food industry) mixed with increasing concentrations of synthetic aragonite rod-like powder of 0, 100, 200 and 300 mg/ml (named WPI0, WPI100, WPI200 and WPI300). FTIR results showed that aragonite was successfully incorporated into the WPI hydrogel network. SEM and micro-CT investigations revealed that aragonite was mainly concentrated near the edges of the composite samples, except in WPI300, which had homogeneous aragonite distribution. The pore diameters ranged from 18 to 778 μm while averaged pore size was the lowest for WPI0 at 30 μm and highest for WPI200 at 103 μm. The mean compression modulus was highest for WPI300 at 3.16 MPa. After 28 days in physiological conditions WPI300 had maximum mean swelling of 4.3% and there was the highest degradation rate for WPI200 and WPI300 and lowest for WPI100 and WPI0. The osteoblast-like MG63 cell metabolic and alkaline phosphatase activities in direct contact experiments with composites increased with increasing aragonite content over 3 weeks. Moreover, the degradation products of these composites were non-cytotoxic and led to mineral-like deposits in extracellular matrix. These WPI-aragonite biocomposite hydrogels are potent candidates for bone repair applications.