To provide a method for producing a thermoplastic resin composition, capable of preventing the scattering of an additive to the outside of a solid phase polymerization vessel accompanying with the decrease of pressure in the solid phase polymerization.

This method for producing the thermoplastic resin composition is characterized in that a tablet-formed additive is used in one or a plural number of additives used in a rotary batch type solid phase polymerization device under a reduced pressure, also among the composition of the additives, the melting point of at least one of them is at or less than the temperature for the solid phase polymerization, the ratio of the diameter to height of the tablet-formed additive is 0.5-2.5 and also the breaking strength of the tablet-formed additive is 3-15 kg.