Abstract: To study the mechanisms whereby cisplatin suppresses survival of human esophageal squamous carcinoma cells, the cytotoxicity of cisplatin in cisplatin-resistant cell line EC109/CDDP and its parental cell line EC109 was measured by cell viability assay. Western blot was used to investigate the protein expression of total p53 and phosphorylated p53 at Ser15. Colony formation assay was employed to evaluate the ability of cells to recover from treatments and form colonies. The results indicated that EC109/CDDP cells were more resistant to cisplatin-induced cytotoxicity than EC109 cells, with the IC₅₀ values of(20. 4±4. 4)μmol/L and(5. 7±0. 1)μmol/L, respectively. Although cisplatin did not alter the total protein level of p53, it obviously increased the phosphorylation of p53 at Ser15. Cisplatin inhibited survival of both EC109/CDDP and EC109. Notably, inhibition of p53 by Pifithrin-α significantly promoted the recovery of cisplatin-treated EC109 and EC109/CDDP cells in different degrees. In this respect, p53 signaling pathway was found to be activated in response to cisplatin treatment in both EC109/CDDP and EC109, which may contribute to the cytotoxic effect of cisplatin.