Cantharidin is a natural compound with cardiotoxicity. Cellular senescence and senescence-associated secretory phenotype (SASP) are implicated in chemotherapy-associated cardiotoxicity. We here investigated how cantharidin induced cardiomyocyte senescence. H9c2 cells were treated with cantharidin. Senescence, mitochondrial functions, SASP, NOD-like receptor thermal protein domain associated protein 3 (NLRP3) signaling and AMP-activated protein kinase (AMPK) phosphorylation were examined. Cantharidin inhibited viability and increased expression of senescence-associated β--galactosidase (SA-β-Gal), p16 and p21 in H9c2 cells, suggesting occurrence of senescence. Cantharidin impaired mitochondrial functions evidenced by reduction in basal respiration, ATP levels and spare respiratory capacity. Cantharidin also decreased mitochondrial DNA copy number and down-regulated mRNA levels of cytochrome c oxidase-I, -II and -III. Moreover, cantharidin suppressed activity of mitochondria complex-I and -II. Examinations of SASP showed that cantharidin promoted expression and secretion of SASP cytokines interleukin-1β-, -6 and -8 and tumor necrosis factor-α, associated with activation of NLRP3/caspase-1 pathway. Finally, cantharidin suppressed AMPK phosphorylation. AMPK activator GSK621 abrogated the up-regulation of SA-β--Gal, p16 and p21 and counteracted the activation of NLRP3 and caspase-1 in cantharidin-challenged H9c2 cells. In conclusion, cantharidin stimulated senescence and SASP in cardiomyocytes through activation of NLRP3 inflammasome and inhibition of AMPK, providing novel molecular insights into cantharidin-induced cardiotoxicity.