Carbonyl compounds generated and accumulated in the peritoneal dialysate can be inactivated or eliminated by a carbonyl compound-trapping agent such as aminoguanidine. Carbonyl compounds generated during sterilization and storage of the peritoneal dialysate can be eliminated by pre-contacting with the trapping agent. Further, it is possible to eliminate carbonyl compounds transferred from the blood to the peritoneal cavity of the patient during peritoneal dialysis treatment, by adding the trapping agent to the peritoneal dialysate or by circulating the fluid through a carbonyl compound-trapping cartridge. Intraperitoneal protein modification by carbonyl compounds is inhibited by the present invention, thereby sufficiently reducing peritoneal disorders associated with peritoneal dialysis treatment.