Silicon nanowire arrays (SiNWAs) were found to have catalytic activities similar to those of biological enzymes catalase and peroxidase. Thus not only can these materials catalyze the decomposition reaction of H2O2 into water and oxygen, but they can also catalyze the oxidation of o-phenylenediamine (OPD), a common substrate for peroxidases, by H2O2. The presence of Si-H bonds and the morphology of the SiNWAs are found to be crucial to the occurrence of such catalytic activity. When the SiNWAs are reacted with H2O2, the data from Raman spectroscopy suggests the formation of (Si-H)(2)center dot center dot center dot(O species) ((Si-H)(2)center dot center dot center dot Os), which is presumably responsible for the catalytic activity. These findings suggest the potential use of SiNWAs as enzyme mimics in environmental chemistry. medicine, biotechnology, and environmental chemistry.