The aim of the study was to use an animal model to investigate the mechanisms by which tranexamic acid (TNA) increases ultrafiltration (UF) volume. Thirty Sprague-Dawley rats were studied in three groups (n = 10, each group). Group 1 was dialyzed with conventional dialysis solution, group 2 with conventional fluid plus low-dose TNA (300 mg/L), and group 3 with conventional fluid plus high-dose TNA (3000 mg/L). A PD catheter was inserted into each animal, and 25 mL of the designated dialysis fluid was injected twice daily for two weeks, starting seven days after surgery. Peritoneal transport properties (PTP) were measured by modified peritoneal equilibration test (PET), and transcapillary ultrafiltration (TCUF) and lymphatic absorption (LA) were determined by using dextran 70 weekly. Histological examinations of the peritoneum were performed at the end of the experiment. Drained dialysate volume (DDV) decreased in all groups; however, a lower reduction in DDV was seen in the TNA groups. PTP increased and TCUF decreased in all groups. LA increased in Group 1, but was unchanged in the other groups. No significant histological changes of the peritoneum were observed in any group. This study confirmed that, in rats, TNA maintained UF volume by reducing LA without serious adverse effects. We may safely use TNA as a "diuretic" for the peritoneal membrane.