Disclosed herein are a gelling agent composed of an isoleucine derivative having a carbazolyl group, and a process for preparing a gelling agent, which comprises reacting an isoleucine derivative having a specific skeletal with a compound having a carbazolyl group in the presence of dichloromethane and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to obtain an isoleucine derivative having a carbazolyl group.