The method for concentrating an oxygen isotope or isotopes of the present invention combines the step of concentrating 17O and/or the step of depleting 18O that utilizes photodissociation of ozone by a laser beam with an oxygen distillation step that concentrates the oxygen isotope. At this time, it is preferable to carry out a step of isotope scrambling in addition to the above. When both a step of concentrating 17O and a step of depleting 18O are carried out, whichever thereof may be done first prior to the other. Also these steps may be placed either before or after the oxygen distillation step. Moreover, at least one of said oxygen distillation step, the concentrating 17O step, the depleting 18O step and the isotope scrambling step is preferably carried out twice or more.