Bulk, supported, and porous perovskite LaCoO3 were prepared and their catalytic performances for CO oxidation were investigated. XRD, FTIR spectroscopy, SEM, TEM, and N2 physisorption measurements were performed to identify their structure, and temperature-programmed desorption of oxygen, temperature-programmed reduction by hydrogen, and X-ray photoelectron spectroscopy were conducted to study their physicochemical properties. With the change from bulk to nanoparticles and further to a porous structure, the series of LaCoO3 samples showed increased oxygen vacancies and improved oxidizing ability, which led to enhanced catalytic performances for CO oxidation. The correlation of the CO oxidation activity with the amount of exposed metal sites indicated that the Co ions should be the active site of the reaction. Comparison of the activation energy supported the changes observed in the activities.