Abstract: The photodynamic effect of the phycocianin excited with a pulsed copper vapour laser on the human colorectal cancer cell line HR8348 was evaluated in our laboratory. The HR8348 cells were incubated in RPMI-1640 medium containing a series concentration of phycocianin (100, 50, 25pg/ ml)，and subsequently subjected to an irradiation with a pulsed copper vapour laser with the wave-length of 620nm and energy of 12 J/cm2, 24 hours after irradiation, the survival rates of the cells as determined with MTT assay were 22.1% ，37. 6% and 89. 7写，respectively, demonstrating a linear doseresponsive effect. Compared with the commercially available photosensitizer chlorophyll II derivative CPD4, phycocianin appeared to be more effective in killing the HR8348 cells. With its sat-isfactory nontoxic photosensitivity. phycocyanin would be a refined photosensitizer for the laser ther-apy for cancer.