The objective of the present invention is to provide a process for simple and efficient preparation of an intermediate compound to synthesize a gadolinium complex having a substituent for improving a retention property in blood time and specificity to an intended organ. The objective of the present invention is also to provide an intermediate compound produced by the said production process. The process for preparation of the diethylenetriaminepentaacetic acid derivative (I): wherein R1 to R5 are independently C1-6 alkyl groups; comprising the steps of: reacting a diethylenetriaminepentaacetic acid pentaester with a halogenated ally compound in an aprotic solvent; removing the excess halogenated ally compound (III); and reacting a reaction product of the diethylenetriaminepentaacetic acid pentaester and the halogenated ally compound with a base in a solvent.