The invention provides a plasma processing method in which plasma etching is performed on a film to be etched by using a mask, the plasma processing method including: a deposition step of depositing a deposition film containing a boron element on the mask while a radio frequency power is supplied to a sample table on which a sample formed with the film to be etched is placed; and an etching step of etching the film to be etched by using plasma after the deposition step.