In this paper, we present measurements of O(D-1) quantum yields of ozone photolysis, phi(lambda), in the wavelength region between 300 and 330 nm and at 355 nm. The data are obtained from an experiment which is based on the reaction of O(D-1) atoms with water and the subsequent detection of the generated OH by laser-induced fluorescence (LIF). Due to the performance of this method, providing a high level of accuracy and precision, it was possible to answer the question concerning the wavelength dependence of the O(D-1) quantum yield in the threshold region. In particular, the value of phi(lambda) at 302.5 nm was determined to be unity, the existence of a saddle point at 315 nm was verified, and the wavelength of the threshold was determined to be between 331 and 333 nm. In addition, measurements performed at 355 nm have shown a negligible contribution to the O(D-1) quantum yield. Thus, it can be deduced that a participation of the spin-forbidden process with the products O(D-1) and O-2((3) Sigma(g)(-)) is unlikely.