The surface tension of supercooled liquid Ni-15%Sn alloy was measured by the electromagnetic oscillating drop method over a wide temperature range from 1368 to 1915K. The maximum supercooling of 265K(0.16TL) was achieved. Over the temperature range investigated, the measured surface tension shows a linear property expressed by σNi-15%Sn=1316.7-1.01(T-TL)mN/m. On the basis of experimental data, the viscosity and the diffusion coefficient of Ni-15%Sn melt were derived, and we also analyzed the activation energy for viscous flow and diffusion.