Rationale: Sustained cardiac hypertrophy often leads to heart failure (HF). Understanding the regulation of cardiomyocyte growth is crucial for the treatment of adverse ventricular remodeling and HF. Cell division cycle 20 (CDC20) is an anaphase-promoting complex activator that is essential for cell division and tumorigenesis, but the role of CDC20 in cardiac hypertrophy is unknown. We aimed to test whether CDC20 participates in the regulation of pathological cardiac hypertrophy and investigate the underlying mechanism in vitro and in vivo. Methods: Male C57BL/6 mice were administered a recombinant adeno-associated virus serotype 9 (rAAV9) vector expressing CDC20 or a siRNA targeting CDC20 and their respective controls by tail intravenous injection. Results: Microarray analysis showed that CDC20 was significantly upregulated in the heart after angiotensin II infusion. Knockdown of CDC20 in cardiomyocytes and in the heart reduced cardiac hypertrophy upon agonist stimulation or transverse aortic constriction (TAC). Conversely, enforced expression of CDC20 in cardiomyocytes and in the heart aggravated the hypertrophic response. Furthermore, we found that CDC20 directly targeted LC3, a key regulator of autophagy, and promoted LC3 ubiquitination and degradation by the proteasome, which inhibited autophagy leading to hypertrophy. Moreover, knockdown of LC3 or inhibition of autophagy attenuated Ang II-induced cardiomyocyte hypertrophy after deletion of CDC20 in vitro. Conclusions: Our study reveals a novel cardiac hypertrophy regulatory mechanism that involves CDC20, LC3 and autophagy, and suggests that CDC20 could be a new therapeutic target for patients with hypertrophic heart diseases.