The photon-to-photoelectron conversion efficiency and the reflectance of a photomultiplier have been measured as a function of the photon incident angle. Appreciably large conversion efficiency and reflectance were obtained for a incident angle near 45 degrees. A calculation was made for an optical model of a photomultiplier. The results were consistent with the experimental results. (c) 2006 Elsevier B.V. All rights reserved.