An isolated alkaline pullulanase Y having .alpha.-amylase activity; a microorganism producing the alkaline pullulanase Y; and a process for producing the alkaline pullulanase Y are disclosed. The alkaline pullulanase Y having .alpha.-amylase activity has its optimum pH at higher alkaline range than conventional alkaline pullulanases and exhibits excellent stability in a wide pH range. Further, the alkaline pullulanase Y has strong resistance to almost all detergent components such as surfactants, chelating agents, proteases for detergents, and the like. Thus the alkaline pullulanase Y can advantageously be used as a detergent component.