The present invention provides 3-hydrazino-2,5-dioxopyrrolidine-3-carboxylates of the formula (I): wherein R1 is a C1-6 alkyl group, etc., R2 is a hydrogen atom or a COOR3 group, wherein R3 is a tert-C4-6 alkyl group, a 2,2,2-trichloroethyl group or a benzyl group in which the benzene ring moiety may be optionally substituted by one or two atoms or groups independently selected from the group consisting of a halogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, a cyano group and a nitro group, and a salt thereof, which are useful as a novel intermediate for preparing tetrahydropyrrolo[1,2-a]pyrazin-4-spiro-3′-pyrrolidine derivatives such as Ranirestat being promising therapeutic agents for diabetic complications in a short process and in an economically advantageous and safe manner, and the process for preparing the same.