Series of Ga-doped Sc2-xGaxW3O12 samples (x=0, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8) were synthesized by solid state reaction at 1100 ℃. Rietveld refinement of the X-ray powder diffraction patterns show that Ga substituted Sc in Sc2-xGaxW3O12 structure successfully. The client component Ga2W3O12 cannot be obtained in this work. The lattice parameters obtained by Rietveld refinement showed that all samples have negative thermal expansion between 25—1000 ℃. Lattice parameters a, c and cell volume of the Sc2-xGaxW3O12 decrease with the increases of Gallium content, but accompanied with the expansion of lattice parameter b. The average volume expansion coefficient also decreases with the increase of the Gallium content. As the temperature increases, the absolute value of the volume expansion coefficients decrease dramatically between room temperature and 300 ℃, but remain almost unchanged between 300 and 800 ℃, and decrease further at the temperature higher than 800 ℃, tending to zero and turning into positive expansion.