A classifier for a cathode active material includes an active material inlet through which a cathode active material mixture that includes an active material powder including lithium composite oxide particles and dust particles is injected, a classifying body having a classifying sieve for classifying the active material powder into a first active material powder and a second active material powder, an upper outlet located at an upper portion of the classifying body so that the dust particles are scattered and discharged from the cathode active material mixture, an active material outlet connected to a central portion of the classifying body to discharge the first active material powder, and a lower outlet connected to a lower portion of the classifying body to discharge the second active material powder of the cathode active material mixture.