Photoisomerization of alpha-(9"-anthryl)ethylspiro[cyclopropane-1,9’-fluorene]-2-carboxylates (An-1 reversible arrow An-2) in an ethanol/benzene 1:1 mixture has been studied by stepwise two-color two-photon excitation methods. Upon selective excitation of the T-1-T-n (n greater than or equal to 2) absorption band of the anthryl moiety, the isomerization takes place and the T-1 population decreases, indicating that the T-2 state of the anthryl moiety is a key state for the isomerization. The quantum yields of the T-1 depopulation in addition to the quantum yields of fluorescence and intersystem crossing have been determined for both An-1 and 2. On the basis of these yields, the detailed reaction mechanism has been established.