A method for producing a resin composition is provided. The method includes melting and kneading a thermoplastic resin having a transition temperature of less than 200° C. and a powder with a twin-screw kneading extruder. The powder is an inorganic filler having an apparent density of 0.1 to 1.5 g/ml. The resin is supplied from a supply port to the extruder, and the powder is supplied from a gravimetric feeder to the extruder through a screw type side feeder. A transport capacity of the side feeder is 2 times or more an effective volume of the powder per unit time. In the extruder, melting and kneading are performed under conditions in which resin pressure in a first kneading zone is 1 MPa or more, and resin pressure in a second kneading zone is less than 3 MPa, and gas is removed from a vent port.