Provided are a preparation method of a resist composition which enables stabilization of a dissolution performance of a resist film obtained from the resist composition thus prepared; and a resist composition obtained by the preparation process and showing small lot-to-lot variations in degradation over time. The process of the present invention is for preparing a chemically amplified resist composition containing a binder, an acid generator, a nitrogenous basic substance and a solvent and it has steps of selecting, as the solvent, a solvent having a peroxide content not greater than an acceptable level, and mixing constituent materials of the resist composition in the selected solvent.