A novel method to prepare narrowly dispersed silver nanoparticles in hydrogel is reported. Gelator, the conjugate of cholic acid and polyethylene glycol 400, was used to form the gel, and it acted not only as the stabilizer preventing the silver particles from further growth and aggregation, but also as a reducing agent. Through this single-step synthesis, narrowly dispersed Ag nanoparticles were obtained in the hydrogel system at ambient temperature. The approach here is simple, economical, and environmentally benign.