An internal Brewster guided-mode resonance (GMR) filter is designed. For this kind of GMR filter, the Brewster reflection occurs at the interface of grating/waveguide layers rather than at the interface of air/grating layers. At Brewster angle of 60\circ the GMR filter owns almost 100% reflection at the resonance wavelength of 800 nm with the full-width at half-maximum (FWHM) of 0.2 nm. Its angle response changing with the fabrication deviation is also discussed.