Activation of the intrinsic regenerative potential of adult mammalian hearts by promoting cardiomyocyte proliferation holds great potential in heart repair. CAND1 (Cullin-associated and neddylation-dissociated protein 1) functions as a critical regulator of cellular protein homeostasis by fine-tuning the ubiquitinated degradation of specific abnormally expressed protein substrates. Here, we identified that cardiac-specific transgenic overexpression of CAND1 reduced the infarct size, restored cardiac function, and promoted cardiomyocyte proliferation after myocardial infarction in juvenile (7-day-old) and adult (8-week-old) mice. Conversely, CAND1 deficiency blunted the regenerative capacity of neonatal hearts after apex resection. MS and functional verification demonstrated that CAND1 enhanced the assembly of Cullin1, FBXW11(F-box/WD repeat-containing protein 11), and Mob1b (Mps one binder kinase activator 1b) complexes, and thus promotes the degradation of Mob1b. The ubiquitination of Mob1b occurred at K108 and was linked by K48 of ubiquitin. Mob1b deletion partially rescued the loss of regenerative capacity in neonatal hearts induced by CAND1 deficiency and improved cardiac function in adult mice post-MI. Moreover, CAND1 promoted the proliferation of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Our data demonstrate that CAND1 promotes cardiomyocyte proliferation via FBXW11-mediated K48-linked ubiquitination degradation of Mob1b, and improves heart regeneration after cardiac injury. The findings provide a novel strategy to promote cardiac regeneration and repair. Schematic diagram of the role of CAND1 in regulating ubiquitination and degradation of Mob1b and cardiomyocyte proliferation and heart regeneration. Under CAND1-High condition, CAND1 promotes the incorporation of Cullin1, FBXW11, and Mob1b complexes, and accelerates SCF-mediated K48-linked ubiquitination of Mob1b at the K108 site, which leads to the degradation of Mob1b and thus suppresses the Hippo signaling pathway and facilitates cardiomyocyte proliferation and heart regeneration post-MI.