The OH(A-X) and OD(A-X) emission spectra have been measured by 17 eV electron impact on the mixtures of H2O and D2O with several mixing ratios. The intensity ratio of the OH(A-X) emission to that of OD(A-X), q, in the spectra of the mixture has been estimated using the OH(A-X) and OD(A-X) spectra obtained from pure H2O and pure D2O. As a result, q is proportional to the ratio of the H-atom quantity to the D atom in the mixture, indicating that q is independent of the fraction of HOD in the mixture. The following emission intensity ratios are obtained, sigma(HOD-->OH)/sigma(HOD-->OD)=sigma(H2O-->OH)/sigma(D2O-->OD)=0.53+/-0.02, sigma(D2O-->OD)/sigma(HOD-->OD) = 1.88 +/- 0.24, where sigma(HOD-->OH) means the total emission cross section of OH(A-X) by electron impact on pure HOD, and the others are similar.