This paper deals with the resolving power of anthracene single crystal for electrons of monochromatic energy. As the electrons, internal conversion electrons emitted from cesium-137 and mercury-203 are used. Electrons impinging on the crystal are collimated by aluminum collimator, 8mm in diameter and 5mm in thickness. The crystal is the one that was used in a previous work (T. WATANABE: J. App. Phy., Japan, 28, 377, (1959)), and its side faces being now covered with filter paper to reflect the light produced in the crystal. The use of collimator and reflector is found to improve the energy resolution. To see the effect of gamma-rays on pulse height distribution curve, an acrylic resin plate, served as the absorber of beta-rays and electrons, is inserted between the source and the crystal. On the assumption that about 30% of light produced in the crystal falls on the photocathode of photomultiplier tube, energy resolution calculated by using E. Breitenberger's equation agrees with that obtained by experiment, but if 100% of light is assumed to fall on the cathode, calculated value is 14% against 14% in the case of 30% efficacy of light, on cesium-137 source.