Glutathione S-transferase P1 (GSTP1) is known as a xenobiotic enzyme through conjugation of glutathione and also as an inhibitor of Jun N-terminal kinase (JNK). We intended to investigate whether GSTP1 affects chemoresistance against camptothecin in human lung adenocarcinoma cells. Camptothecin induced GSTP1 expression. Downregulation of GSTP1 increased necrosis induced by camptothecin in A549 cells but not in PC-14 and RERF-LC-KJ cells. This phenomenon in A549 cells was hardly changed by JNK inhibitor SP600125 but was almost diminished by l-buthionine-sulfoximine. These results suggest that GSTP1 has protective effects against camptothecin-induced necrosis in subset of human lung adenocarcinoma through glutathione conjugation.