The mouse tumor cell S180 and human liver carcinoma cell SMC 7721 cells were first treated with R-PE and its subunits (alpha, beta, gamma subunits), then irradiated with Argon laser (496 nm, 28.8 J/cm2). Survival rate was measured by MTT method. In order to compare the phototoxicity in normal cells, the mouse marrow cells were treated with photofrin II and beta-subunit, irradiated with 45 J/cm2 of light; survival rate was also measured by MTT method. The result showed that R-PE subunits had better PDT effect on s180 cells than R-PE and lower phototoxicity in marrow cells than photofrin II. Flow cytometric analysis showed that PDT results in a growth inhibition and a G0-G1 cell cycle arrest in SMC 7721 cells. The tumor cells inhibited by PDT in vivo were morphologically observed by TEM, the tumor cell death was due to the occlusion of tumor blood vessels and inducement of cell programmed death in nuclei. Therefore, with the advantage in special fluorescence activity, low molecular weight, good light absorbent character and weak phototoxicity, R-PE subunit is an attractive option for improving the selectivity of PDT.