High surface area M (M = La, Pr, Nd, and Pm)-doped ceria nanoparticles have been synthesized by the citric acid-aided sol gel method to check their catalytic activity for carbon monoxide (CO) oxidation. BET analysis revealed high specific surface areas of M -doped CeO2 catalysts (similar to 190-198 m(2) g(-1) XRD and TEM showed 3-6 nm size of particles of M-doped CeO2 catalysts. Raman results showed the highest amount of oxygen vacancy possessed by La-doped CeO2 compared to other dopants. The catalytic activity for CO oxidation follows the order La-CeO2 > Pr-CeO2 > Nd-CeO2 > Pm-CeO2 > CeO2. La-doped CeO2 exhibited the highest catalytic activity (T-50 - 170 degrees C) due to the higher quantity of oxygen vacancies, larger specific surface area, smaller particle size, and enhanced oxygen storage capacity (OSC) comparison to other dopants. This catalyst also showed an excellent stability for CO oxidation reaction for a time-on-stream of 50 h.