The differential excitation cross section of O(1D) from the ground state has been measured at 20 eV electron impact by a crossed-beam method. The angular range covered was from 30 to 150 degrees. Atomic oxygen was generated by a thermal dissociation method (iridium oven). The measured total excitation cross section is (1.5¿0.7)¿10-17 cm2 which agrees, within the accuracy of the measurement, with the theoretical value (1.7¿10-17 cm2) calculated by Henry et al. (1969).