Spectrophotometric data for six planetary nebulae in the direction of the galactic bulge were used to derive the properties of the interstellar reddening for this region. The observed nebular continuum was compared with theoretically predicted nebular continuum and the interstellar reddening was evaluated from she differences. The derived reddening function for each nebula shows generally good agreement with the Whitford reddening law in long wavelengths of visible region. However, there exist significant deviations from the standard law in ultraviolet, which may be explained by either different composition or different size distribution of the dust grains lying toward the galactic center. A rough estimate suggests R = 1.5 similar to 2.0, which is significantly smaller than the standard value of R = 3.