A plasma processing method is provided for reducing dimensions of a film to be etched from patterned dimensions, and is capable of reducing dimensions without causing deformation or collapse of the film to be etched. A plasma processing method for trimming a tantalum film by plasma etching using a resist, an antireflective film disposed under the resist, and a mask film disposed under the antireflective film, includes the steps of trimming the antireflective film and the mask film by plasma etching with the resist as a mask; removing the resist and the antireflective film subjected to the trimming, by plasma; and trimming the tantalum film by plasma etching with a mask film obtained after the resist and the antireflective film subjected to the trimming are removed by plasma, as a mask.