p53 is the guardian of the genome integrity and the degradation of p53 protein is mediated by MDM2. Here we report that USP3 interacts with p53 and regulates p53 stability. Depletion of USP3 lead to accelerated degradation of p53 in normal cells thereby enhanced cell proliferation and transformation. Reconstitution of wildtype USP3, but not the USP3 C168S mutant, restored the stability of p53 protein and inhibited cell proliferation and transformation. These findings suggest that USP3 is an important regulator of p53 and regulates normal cell transformation. (C) 2017 Elsevier Inc. All rights reserved.