In order to clarify the efficacy and safety of using a crystallized lactulose (CL) preparation to treat constipation in hemodialysis (HD) patients, we orally administered the CL preparation for 4 weeks to 28 HD patients, who had previously been treated with other laxatives for chronic constipation. The frequency of satisfactory spontaneous defecation in the 4th week treatment had significantly increased (p=0.03). In addition, stool consistency was significantly improved in the 1st, 3rd, and 4th week of the treatment (p<0.05, p<0.01, and p<0.01, respectively). Regarding the severity of constipation, the number of patients with grade 0 constipation significantly increased from none to 11 after 4 weeks’ treatment (p<0.001). In addition, the levels of blood urea nitrogen and creatinine were significantly decreased by CL-treatment (p<0.01 after 2 weeks’ treatment, p<0.05 after 4 weeks’ treatment, respectively). With regard to adverse reactions, no deaths occurred, and only one patient developed mild diarrhea, which disappeared after the CL treatment was discontinued. The above results demonstrated that CL is useful for treating chronic constipation in HD patients.