Objective To study the effects and mechanism of norcantharidin ( NCTD) on proliferation and apoptosis of NB4 and K562 human leukemic cells by regulating phosphoprotein phosphatase 5 catalytic ( PPP5C). Methods PC3. 1 and PPP5C-PC3. 1 plasmids were electroporated into NB4 and K562 cells. Stable NB4 and K562 cell lines were selected with geneticin (G418). Protein and mRNA expression levels of PPP5C were measured by Western blot and RT-qPCR, respectively. Proliferation, migration, and apoptosis of NB4 and K562 cells were determined by a CCK-8 assay, transwell assay, and Live & Dead TM animal cell viability / toxicity detection kit, respectively. NB4 and K562 cells were divided into 0 μg / mL NCTD group and various NCTD dose groups, and cultured in RPMI 1640 medium containing 0,8, 16, or 32 μg / ml NCTD. The Live & Dead TM animal cell viability / toxicity detection kit measured the numbers of dead and live cells, and cell morphology was observed under a microscope. Western blot was used to measure protein expression levels of caspase 3, Cleaved caspase 3, JNK, p-JNK, p38, p-p38, and α-Tubulin. Results Proliferation, migration,and apoptosis of NB4 and K562 cells were enhanced by overexpression of PPP5C. Compared with 0 μg / mL NCTD group,NCTD promoted apoptosis in a dose-dependent manner. PPP5C overexpression antagonized the killing effect of NCTD on leukemic cells. Mechanistic investigations showed that PPP5C reduced the protein level of p-JNK by dephosphorylating and regulating the expression of apoptosis-related protein Cleaved caspase 3. Conclusions NCTD promotes apoptosis of NB4 and K562 cells and inhibits their proliferation by inhibiting PPP5C.