The characteristic of thin film narrowband filters used in tilted incidence is described. The wavelength shift to shorter wavelength in a low index spacer filter for p polarization component is larger than that for s polarization component when filter is tilted. On the contrary, the shift in a high index spacer filter for p component is less than that for s component. Therefore the passbands of a tilted filter can be centered at the same wavelength for two polarization modes by means of using high and low index materials for a spacer, or selecting a moderate index material instead of a spacer. Designs of DWDM filters used for incident angle of 20°are presented, and the experimental results are discussed.