The compressive deformation behavior of extruded Mg–Y–Zn alloys containing long-period stacking ordered (LPSO) phase was investigated through in situ neutron diffractionNeutron diffraction measurements and quasi-in situ characterizationCharacterization of microstructure evolutionMicrostructure evolution during compression tests. The initial microstructureMicrostructure of the extruded Mg–Y–Zn alloys formed a multimodal microstructureMicrostructure consisting of dynamically recrystallized (DRXed) αMg grains with random crystallographic orientation and worked αMg and LPSO grains with a strong fiber texture where the \(\left\langle {{1}0\overline{1}0} \right\rangle\) direction was parallel to the extrusion direction. The in situ neutron diffractionNeutron diffraction measurements revealed that { \(10\overline{1}2\) } twin and basal  \(\left\langle a \right\rangle\)  slip were activated under ~ 227 MPa and ~ 347 MPa compression, respectively. This indicates that microscopic yielding occurred before macroscopic yielding at 354 MPa, which was defined by a 0.2% proof stress. By contrast, prismatic  \(\left\langle a \right\rangle\)  slip was estimated to have occurred immediately after macroscopic yielding. MicrostructureMicrostructure characterizationCharacterization revealed that { \(10\overline{1}2\) } twinningTwinning mainly occurred in worked αMg grains. The component stress for each constituent region was estimated based on the results of the twin completion fraction evolution during compressive deformation. The DRXed αMg grains exhibited higher grain stresses than the worked αMg grains at the macroscopic yielding, while the worked αMg grains exhibited large work hardening after yielding and higher grain stresses than the DRXed αMg grains just before fractureFracture. Even within the same hexagonal close-packed Mg matrix phase, different crystal orientations result in significant variations in deformation behavior.