Optical microscope(OM), electron back scattering diffraction(EBSD) and uniaxial tension and compression tests were carried out to investigate the effect of Y content (1，5 wt.%), extrusion temperature(ET) and extrusion ratio(ER) on the microstructure and tension-compression deformation behavior of extruded Mg-Y alloy bars. Results show that the grain change from typical bimodal structure to small ,homogeneous and fully dynamic recrystallized grains with increasing Y content from 1% to 5%(ET=300℃, ER=9). The average grain size of cross section (ED plane) and longitudinal section (TD plane) of two alloy bars are close and approximately 14.1±1.9μm~16.5±1.6μm. As a result of dramatically weakened basal plane fiber texture and decreasing texture intensity (~53%), the room temperature tensile yield strength (TYS) decreases from 173±3MPa to 125±6MPa while fracture strain remarkably raises from 11.0±2.1% to 31.0±1.2%. Furthermore, the tension-compression asymmetry changes from common (CYS/TYS=0.8) to inverse (CYS/TYS=1.10) with increasing of Y content. With the increasing extrusion ratio from 9 to 32 (ET=300℃),the TYS of Mg-1Y alloy bars drastically increases to 242±1MPa (~40%), which may be closely related to fully dynamic recrystallization, finer grain size (~10.1±1.4μm) and obviously weakened basal plane fiber texture (~75%). The increasing extrusion temperature (300~400℃) has little effect on grain size and tension mechanical properties of Mg-1Y alloy bars (ER=32) while compression yield strength (CYS) raises to 236±9MPa (~15%), the value of CYS/TYS changes from 0.85 to 1.02 which means alloy exhibit tension-compression symmetry. Y content has an obvious influence on the deformation behavior of extruded Mg-Y alloy bars. All of the extruded Mg-1Y alloy bars show sigmoid compression stress-strain curve while no similar phenomenon in Mg-5Y alloy bar is observed. Observation of microstructure after compression suggests that this phenomenon is closely related to twining dominant deformation mechanism.