Because of the high stability and low cost, nanomaterials performed as alternative artificial enzymes to natural enzymes have attracted much interest and been widely applied in bioanalysis, catalysis and environment in the past decades. In this work, Pt/CeO2 nanocomposites were designed as novel nanozyrnes and synthesized by a surfactant free method. The Pt nanoparticles with an average size of 2.6 +/- 0.4 nm were uniformly decorated on the surface of CeO2 nanorods. The peroxidase-like activity of Pt/CeO2 nanocomposites was verified by several chromogenic substrates in the presence of H2O2. Compared to CeO2 nanorods and Pt nanoparticles, the as-prepared Pt/CeO2 nanocomposites exhibited enhanced enzymatic activity due to the strong metal-support interaction. The steady-state kinetic results demonstrated that the catalytic behavior of Pt/CeO2 nanocomposites consisted with the typical Michaelis-Menten kinetics. The mechanism studies illustrated that the Pt/CeO2 nanocomposites acted as electron transfer mediators during the catalytic process rather than promoting the generation of hydroxyl radical. Based on the intrinsic inhibition effect of ascorbic acid (AA) on oxidation, a simple, sensitive and selective colorimetric assay for detection of AA was established with a good linear relationship (0.5-30 mu M) and a low limit of detection (80 nM). Further applications of the present system for AA detection in real samples have been also successfully demonstrated, suggesting that the Pt/CeO2 nanocomposites with facile synthesis, high stability and high peroxidase-like activity exhibited promising applications in biomedical fields.