Abstract The photoreduction of acridine has been investigated in three kinds of mixed solvents, benzene-isopropanol, benzene-methanol and benzene-cyclohexane, all in aerated and deaerated conditions. The following general tendensies have been found for the plot Φrel vs. mole fraction. It is approximately linear or slightly concave upward for molecular mechanism, while convex upward for radical mechanism. This indicates that for molecular mechanism a cage model trapping two radicals (e.g. C-radical and alcohol radical) is unsuitable while one act process involving two reactive sites is suitable.