Molybdenum　dichalcogenides　MoX2　(X　=　S,　Se)　have　been　found　to　possess　intrinsic　peroxidase-like　activity.　However,　molybdenum　oxides　(MoO2)　as　peroxidase　mimetics　have　not　been　exploited　yet.　Herein,　MoO2　nanoparticles　were　synthesized　by　a　simple　hydrothermal　method　and　found　to　possess　the　peroxidase-like　activity　for　the　first　time.　MoO2　nanoparticles　could　catalyze　the　oxidation　of　3,3′,5,5′-tetrametylbenzidine　(TMB)　by　H2O2　to　produce　a　blue-color　product　(oxTMB).　The　catalytic　property　and　mechanism　were　investigated　by　stead-state　kinetics　experiment　and　free　radicals　scavenging　experiment,　respectively.　Acetylcholinesterase　(AChE)　could　catalyze　the　hydrolysis　of　acetylthiocholine　chloride　(ATCh)　into　thiocholine　(TCh),　which　could　reduce　oxTMB　to　decrease　the　absorbance　in　solution.　In　the　presence　of　AChE　inhibitor　tacrine,　the　generation　of　TCh　was　inhibited　and　the　absorbance　was　preserved.　Based　on　these　properties,　a　colorimetric　assay　method　was　developed　for　AChE　inhibitor　tacrine.　This　work　not　only　broadens　the　application　of　the　peroxidase　mimetics,　but　also　overcome　the　disadvantages　of　traditional　methods　such　as　expensive,　complex　and　vulnerable　to　background　interference　for　colorimetric　assay　of　AChE　inhibitor.　©　2018　Elsevier　B.V.