A method for producing a resin composition, comprising melting and kneading a thermoplastic resin having a transition temperature of less than 200°C and a powder with a twin-screw kneading extruder, wherein the powder is one or more powders selected from the group consisting of an inorganic filler having an apparent density of 0.1 to 1.5 g/ml and a thermoplastic resin powder having an apparent density of 0.1 to 1.0 g/ml and a transition temperature of 200°C or more, the twin-screw kneading extruder comprises a supply port, a first kneading zone, a screw type side feeder to which a gravimetric feeder is connected, a second kneading zone, and a vent port in order from an upstream side, the thermoplastic resin having a transition temperature of less than 200°C is supplied from the supply port to the twin-screw kneading extruder, the powder is supplied from the gravimetric feeder to the twin-screw kneading extruder through the screw type side feeder, melting and kneading are performed, and gas is removed from the vent port, characterized in that the transport capacity of the screw type side feeder is 2 times or more the effective volume of the powder supplied from the gravimetric feeder to the screw type side feeder per unit time, wherein the transport capacity is the product of space volume fed forward while the screw of the screw type side feeder makes one revolution and the number of revolutions of the screw, and the effective volume is a value obtained by dividing the weight of the powder supplied from the gravimetric feeder to the screw type side feeder per unit time by an apparent density of the powder, and the melting and kneading are performed under conditions in which resin pressure in the first kneading zone is 1 MPa or more, and resin pressure in the second kneading zone is less than 3 MPa. the powder is one or more powders selected from the group consisting of an inorganic filler having an apparent density of 0.1 to 1.5 g/ml and a thermoplastic resin powder having an apparent density of 0.1 to 1.0 g/ml and a transition temperature of 200°C or more, the twin-screw kneading extruder comprises a supply port, a first kneading zone, a screw type side feeder to which a gravimetric feeder is connected, a second kneading zone, and a vent port in order from an upstream side, the thermoplastic resin having a transition temperature of less than 200°C is supplied from the supply port to the twin-screw kneading extruder, the powder is supplied from the gravimetric feeder to the twin-screw kneading extruder through the screw type side feeder, melting and kneading are performed, and gas is removed from the vent port, characterized in that the transport capacity of the screw type side feeder is 2 times or more the effective volume of the powder supplied from the gravimetric feeder to the screw type side feeder per unit time, wherein the transport capacity is the product of space volume fed forward while the screw of the screw type side feeder makes one revolution and the number of revolutions of the screw, and the effective volume is a value obtained by dividing the weight of the powder supplied from the gravimetric feeder to the screw type side feeder per unit time by an apparent density of the powder, and the melting and kneading are performed under conditions in which resin pressure in the first kneading zone is 1 MPa or more, and resin pressure in the second kneading zone is less than 3 MPa.