– Ubiquitin specific peptidase 30, also known as USP30, is a deubiquitinating enzyme that is embedded in the mitochondrial outer membrane. Depletion of USP30 expression by RNA interference induced elongated and interconnected mitochondria, depending on the activities of the mitochondrial fusion factors mitofusins, without changing the expression levels of the key regulators for mitochondrial dynamics. Mitochondria were rescued from this abnormal phenotype by ectopic expression of USP30 in a manner dependent on its enzymatic activity. USP30 participates in the maintenance of mitochondrial morphology, a finding that provides new insight into the cellular function of deubiquitination.