8-hydroxyquinoline complexes of La(III) Gd (III) and Tb (III) were synthesized and the photoacoustic (PA)spectra of these complexes were measured in the region of 300-800nm at room temperature. The PA spectra and excitation spectra are compared and interpreted. It is observed that the photoacoustic spectra and the excitation spectra behave complementarily. The different fluorescence properties of the complexes and the relaxation process models are studied by the photoacoustic amplitude and phase spectra. It is confirmed by the PA phase spectrum that the PA absorption of pi-pi* transition of Tb (Ox)3 complex is dominantly contributed by the slow radiationless relaxation which is due to inner-molecular energy transfer.