The dynamic viscosities of Cu-Sn alloys with different compositions were measured at the same superheat temperature using an oscillating-cup viscometer. It has been found that the viscosities of Cu-Sn melts increase with decreasing temperature and fit well with Arrhenius equation. At the same superheat temperature, it is found that the viscosity is higher around the phase of beta (Cu5Sn), and the highest at Cu-25wt%Sn. When the tin concentration is in the range of 20-40wt%, the average rate of increasing viscosity with the decreasing temperature is faster, and the maximum appears at Cu-25 wt%Sn. (c) 2006 Published by Elsevier B.V.