In the present study, nanocomposite hydrogels composed of alginate-gelatin-nanohydroxyapatite were fabricated using oxidized alginates. We investigated the effect of oxidation conditions on the properties of nanocomposite hydrogels. Alginate was oxidized by sodium metaperiodate at different initial solution concentrations (1, 2 and 5%), while the ratio of sodium metaperiodate to number of alginate's repetitive units was fixed at 60 mol% for all samples. To prepare nanocomposite hydrogels, nanohydroxyapatite, synthesized by precipitation method, was added to the alginate and gelatin solution. The results showed that higher concentration of alginate solution during oxidation step resulted in higher degree of oxidation but lower yield of oxidized alginate. Rheological results obtained at oscillatory shear mode and linear viscoelastic region, revealed the lower storage modulus and complex viscosity in hydrogel samples prepared using highly oxidized alginate. In other words, the initial concentration of alginate solution strongly affects the oxidization reaction yield and microstructure of oxidized alginate which is reflected in rheological behavior.