We conducted a series of in vitro experiments to evaluate the anticancer effect of photodynamic therapy using hypericin and 532㎚ DPSS (diode pumped solid state laser). The cultured KB cells were treated with serial concentrations of hypericin ranging from 0.01㎍/㎖ to 5㎍/㎖ (two-fold dilution) with variable laser dosage (10J, 20J, 30J). The cell viability was evaluated by MTT assay. The type of cell death was detected by fluorescent microscope using Hoechst 33342 / PI (propidium iodide) stain methods. In this study, IC50 value with hypericin-mediated PDT with 10J DPSS laser was 35 ng/ml. The maximum cytotoxicity with Photofrin II-based PDT was observed at high drug concentrations(> 90 ng/ml) independent with laser dose. And the in vitro PDT effects depended on the laser dose and drug concentrations were displayed by the difference in the type of cell death, namely apoptosis or necrosis. According to this result, the hypericin based photodynamic therapy with DPSS laser was effective photodynamic therapy.