A plasma ashing method is used for removing a patterned resist film in a processing chamber after etching a portion of a low-k film from an object to be processed in the processing chamber by using the patterned resist film as a mask. The method includes a first step of supplying a reaction product removal gas including at least CO2 gas into the processing chamber, generating plasma of the reaction product removal gas by applying a high frequency power for the plasma generation, and removing reaction products deposited on an inner wall of the processing chamber; and a second step of supplying an ashing gas into the processing chamber, generating plasma of the ashing gas by applying a high frequency power for the plasma generation, and removing the resist film.