An object of the present invention is to provide a process for producing a thermoplastic resin composition with a further improved hue, containing a neutralizing agent, and a compound (I).There is provided a process for producing a thermoplastic resin composition, comprising a second step of melting-kneading a melting-kneaded product obtained in a first step, and a compound (I). (wherein two R1s, two R2s, R4 and R5 each represent independently a hydrogen atom, an alkyl group etc., two R3s each represent independently a hydrogen atom or an alkyl group, X represents a single bond, a sulfur atom or a —CHR6— group, wherein R6 represents a hydrogen atom, an alkyl group etc., A represents an alkylene group or a *—COR7— group, wherein R7 represents a single bond or an alkylene group, and a symbol * represents a bond with an oxygen atom of a >P—O— portion,one of Y and Z represents a hydroxyl group, an alkoxy group or an aralkyloxy group, and the other of Y and Z represents a hydrogen atom, or an alkyl group.)