A spectral purity Al/Yb/Al filter for the wavelength range of 50 to 100 nm has been designed, fabricated, and characterized. The spectral analysis and transmittance measurements were performed in the wavelength range of 50 to 80 nm and 50 to 100 nm. The spectral analysis measurement results show that high-order harmonics greater than 10 nm can be efficiently suppressed. Transmittance measurement results show that the filter has the ability of harmonic suppression in the wavelength range of 50 to 95 nm. The fitting result of the transmittance measurement result indicated that lower measured transmittance was mainly caused by the interdiffusion and oxidation of the filter.