Using two-beam interference lithography and dry etching, we fabricated a mid-IR wire-grid polarizer consisting of a $350\mathrm{nm}$ pitch WSi grating on an ${\mathrm{Y}}_2{\mathrm{O}}_3$ ceramic substrate, which has wider transparency than sapphire. The transmittance of TM polarization was greater than 70% in the $3–7\mathrm{\mu m}$ wavelength range without antireflection films, and the extinction ratio was over $20\mathrm{dB}$ in the $2.5–5\mathrm{\mu m}$ wavelength range. The wire-grid polarizer with the ${\mathrm{Y}}_2{\mathrm{O}}_3$ ceramic substrate provides high durability and good IR transparency.