In situ neutron diffraction measurements during compressive and tensile tests of an as-cast Mg₉₇Zn₁Y₂ alloy consisting of α phase (αMg) as the matrix and a long period stacking ordered phase (LPSO) with 25 vol%, were performed to understand deformation behavior of each phase and to monitor the occurrence of kinking during deformation. The deformation modes at the beginning stages of compressive and tensile tests below the applied true stresses of 130 MPa were quite similar. The LPSO grains yielded possibly via kinking during compressive deformation above the applied true stress of about 137 MPa. The stress partitioning among αMg grains was observed larger in the compressive deformation than in the tensile deformation, that might be due to the large load sharing of αMg grains as a result of the yielding of LPSO grains during compressive deformation.