There is provided a technique for producing a quinacridone solid solution pigment, the technique making it possible to obtain a quinacridone solid solution pigment which produces a colored product having high chroma and a bluish hue, more preferably which has controlled particle diameters. Specifically, a method for producing a quinacridone solid solution pigment, the method including a crude quinacridone solid solution production step of subjecting a diarylaminoterepththalic acid and a dialkylarylaminoterephthalic acid to a co-cyclization reaction in polyphosphoric acid, thereby obtaining a water-containing crude quinacridone solid solution containing a solid solution of an unsubstituted quinacridone and a 2,9-dialkylquinacridone, the solid solution containing water, a drying step of drying the water-containing crude quinacridone solid solution to reduce the water content to less than 1% and obtain a powdery, crude quinacridone solid solution, and a pigmentation step of heating the powdery, crude quinacridone solid solution in a liquid medium that cannot dissolve the crude quinacridone solid solution.