It is well known on Pb-Sn solders that the maximum spreading on a copper plate is obtained at near eutectic composition of the solder, and the maximum equilibrium rising height in vertical capillary copper joints or the maximum penetration coefficient in horizontal capillary copper joints are obtained respectively at pure tin component of the solder. But, the adequate cause of difference in these phenomena is not known at presentn. This investigation was made to clear the cause. The results obtained are as follows; Institute of OsakaUniv.