Abstract: Objective: Photodynamic therapy （PDT） has become an important new modality in cancer treatment. In order to obtain a better understanding of the mechanisms of apoptpsis induced by PDT. Methods: Cultured GLC-82 cells were loaded with fluo-3/AM fluorescence probes, and the changes of intramyocytic Ca²⁺ concentration were examined by laser scanning confocal microscopy. Results: there were negligible changes of intracytoplasmic calcium concentration of GLC-82 cells after laser irradiation alone. There were remarkble changes of intracytoplasmic calcium concentration of GLC-82 cells after laser irradiation. Conclusion: it is sensitive, rapid, simple and most effective method for real time quantitation of intracellular free calcium.