Density and viscosity of Ni–Ti melts were measured under high-vacuum conditions using an electrostatic levitation technique. The density of Ni–Ti melts can be expressed as a linear function of temperature. The variation of viscosity of Ni–Ti melts with temperature can be reproduced by an Arrhenius function. The excess volume was obtained from the density results and is discussed using the thermodynamic functions of enthalpy of mixing and excess Gibbs energy. Viscosity shows a positive deviation from linear additivity. From comparison with theoretical models, the viscosity is roughly reproduced by Kozlov's model. The viscosity of Ni–Ti melts is possibly influenced by formation of clusters, which form based on congruently melting compounds.