AIM: To investigate the effects of photodynamic therapy on cytokinetics, DNA content and surviving cell fraction of colonic adenocarcinoma cells. METHODS: On the basis of cell culture, after adding verapamil, the effect on the cell cycle, DNA content and surviving cell fraction in photodynamic therapy were studied using fluorescence spectrophotometer, flow cytometer and MTT assay et al. The results were analyzed with SPLM statistical software. RESULTS: After adding PSD(PSD-007,derived from hematoporphy derivative), these intracellular PSD levels of 4.8 and 16 hours exposure increased significantly as compared with that of the adjacent former at the same group respectively, but no significant difference of PSD levels were seen between 16 hours and 24 hours in the same group. The intracellular PSD contents of group PSD and group PSD+Ver had a strong and inverse relationship with surviving cell fractions respectively after photodynamic therapy. The cellular cycle and DNA content were not affected by verapamil alone (0.02 g/ml), but S and G1 phase cells were decreased, G2+M phase cells and DNA contents were increased significantly in group PSD+Ver as compared with that of group PSD. CONCLUSION: Verapamil can increase the intracellular photosensitizer content and strengthen the killing power, which affects the cycle and DNA content of colonic adenocarcinoma cells in photodynamic therapy.