An optical-resolution photoacoustic microscope with modulated CW laser diodes allowing multi-channel imaging is presented that can be used for both imaging biological tissues and for targeted photo-dynamic therapy (PDT) varying the optical power and exposure time. The effects of this therapy are immediately monitored in order to optimize the time of irradiation. After the description of the experimental setup, in vitro and in vivo applications are presented on a synthetic sample and on the mouse ear using hemoglobin as endogenous and methylene blue as exogenous dye for imaging and PDT, respectively.