Absolute differential excitation cross sections of atomic oxygen (3P-1D transition) by electron impact have been measured by a crossed-beam method. Atomic oxygen was generated by a thermal dissociation method. The energy and angular range covered were from 7 to 30 eV and from 30¿ to 150¿, respectively. A few theoretical results were compared with the present measurements and they are in good agreement with the experimental results within the accuracy of the measurement.