The shape of dendrite and arm spacing are dependent on the condition of casting. The dendritic structure and variation in concentration of the solute element affect in mechanical properties. Accordingly deeper understanding of the factor affecting the solidification of casting and the resultant segregation are needed. The results obtained from this study are as follows: 1) The dendrites of Cu-4∼12% Sn alloy grow like plate within the range of the cooling rate obtained by this experiment. 2) The relationship between the primary dendrite arm spacing, the content of Sn and cooling rate was obtained as follows: dp=K√Co/Va dp: primary dendrite arm spacing(mm) 3) The secondary dendrite arm spacing increases with decreasing cooling rate, but is little affected by Sn content. This relationship is obtained as follows: log ds=-0.255 log Va＋2.35 ds: Secondary dendrite arm spacing (mm) 4) The eutectoid phase (α＋o⌒) precipitates independent or the cooling rate in Cu-10 and 12% Sn alloys, but in Cu-8% Sn alloy it precipitates at locations of low cooling rate, and is not observed in Cu-4 and 6% Sn alloy.