In order to clarify the deformation behavior under the conditions of multiple slip activations, the plane strain compression tests were carried out on single crystals of Ni/Ni3Al two-phase (Ni-18 at.%Al) alloys. The flow behaviors were strongly dependent on the initial crystal orientations and were found to be divided into two types depending on the operative number of slip planes. When slip (s) on 1 or 2 slip planes were activated, the work-hardening rates decreased before the critical shear stress levels which was in marked contrast to the case of single phase Ni3Al. On the other hand, the work-hardening rates kept high level in the case of the multiple slips activations on 3 or 4 slip planes. Such flow behaviors were considered to be closely related to differences in deformation between Ni matrix and Ni3Al precipitates.