Abstract: The photodynamic effect of several newly prepared hematoporphyrin derivatives (HPDs) on L₁₂₁₀ and B₁₆ cells in vitro was compared. The cells pretreated with HPDs were exposed to black light and cellular viability was determined by trypan blue exclusion assay. Photofrin II (DHE), a new kind of commercial HPD, was used as a positive control. The results showed that the photodynamic effect of tested HPDs, LF-019, Y-HPD and HA-308 were more potent than that of DHE. The 50% inhibiting concentration (IC₅₀) for DHE was 8.2 μg/ml when the treated B₁₆ cells were exposed to the light for 10 min. However, the IC₅₀ for LF019, Y-HPD and HA-308 were 2.5, 5.3 and 6.2 μg/ml respectively. The effect of LF-019 was 3 times that of DHE. In order to test the reliability of the trypan blue exclusion assay for evaluating the cell killing, the survival times of DBA/2 mice received 1×10⁶ L₁₂₁₀ cells treated with HPDs plus light were measured. The results from these two assays were found to be in good agreement.