Disclosed is a process for preparing a pyrrolidone derivative, which comprises allowing at least one of &ggr;-butyrolactone, 4-hydroxybutyric acid, and a low-molecular polymer of 4-hydroxybutyric acid to react with an alkylamine, wherein (i) the content of a primary amine in said alkylamine is 85% by weight or lower, and (ii) the molar ratio of the total amount of the charged primary and secondary amines to the total amount of the charged &ggr;-butyrolactone, 4-hydroxybutyric acid, and low-molecular 4-hydroxybutyric acid polymers satisfies formula: 1.0≦(A1+A2/2.5)/(B1+B2+B3) wherein A1, A2, B1, B2, and B3 represent the molar amounts of a primary amine, a secondary amine, &ggr;-butyrolactone, 4-hydroxybutyric acid, and low-molecular 4-hydroxybutyric acid polymers, respectively.