By use of polyacrylamide-gel electrophoresis, blood samples from wild and domestic yak are studied for α-Amylase (α-Am) isozymes. It has been found that there are 7 bands in wild yak for α-Am isozyme, but 8 bands in domestic yak. Active boundary of pH in wild yak are wider than that in domestic yak and sensibility to temperature in wild yak are higher than that in domestic yak. Activity and relative content of Am-3 for domestic yak are significantly higher than that for wild yak. The difference of α-Am isozymes between wild and domestic yak provides germplasm material for yak breeding selection.