A systematic investigation concerned with Y1-xMgxTaO4-x/2 (x=0,0.08,0.12,0.16 and 0.20,respectively) ceramics was fabricated by a solid-state reaction method and characterized by X-ray diffraction (XRD),Raman spectroscopy,scanning electron microscopy (SEM) and thermal analysis.XRD spectra display that all of the samples are excellently consistent with the standard XRD spectrum of monoclinic YTaO4 (PDF No.24-1415;space group: I2 (5)).The Raman peaks of the samples doped with Mg2+ just widen slightly compared with those of pure YTaO4,which are in agreement with the results of XRD.The thermal conductivity of dense 7 wt％-8 wt％ yttria-stabilized zirconia (7-8 YSZ) ceramic is about 2.5 W.m-1·K-1 at 900 ℃,while the Y1-xMgxTaO4-x/2 (x =0,0.08,0.12,0.16 and 0.20)ceramics possess lower thermal conductivity in the range of 1.45-1.57 W·m-1·K-1 at 900 ℃,which declines by 35％ compared with that of 7-8 YSZ.The lower thermal conductivities of Y1-xMgxTaO4-x/2 (x =0,0.08,0.12,0.16and 0.20) ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg2+ ions defect complex.However,the thermal expansion coefficients are about 9.0 × 10-6-9.5 × 10-6 K-1 along with the different amounts of Mg2+ doping at 1200 ℃.Compared to the pure sample,the thermal expansion coefficient decreases slightly when the Mg2+ doping amount is over 20％.The systematic investigations on the phase,microstructure,elastic and thermal properties of Y1-xMgxTaO4-x/2 (x =0,0.08,0.12,0.16 and 0.20)ceramics will provide guidance for its application at high temperature,especially as thermal barrier coatings.