Densities of divalent transition metal sulphate, viz. nickel sulphate (NiSO₄), were measured in aqueous and aqueous methanol mixtures (10% to 40% v/v) within concentration range (1×10^-3 to 10×10^-3 mol.dm^-3 ) at different temperatures (298 to 323 K). The acquired data have been analyzed by using the Masson equation for ascertaining apparent molar volume (ϕ_v), partial molar volumes (∅°_𝑣) and experimental slopes (S_v). The obtained results are interpreted in terms of the ion-ion interaction and ion-solvent interactions. Structure making/breaking capacities of electrolytes have been incidental from the Hepler’s criterion i.e. (𝜕²∅°_𝑣/𝜕𝑇²) 𝑃 second derivative of partial molar volume with respect to temperature at constant pressure. Results showed that NiSO₄ in aqueous and aqueous methanol mixtures ranging from 10% to 40% v/v act as structure breaker.