【Abstract】 Objective To assess the effect and mechanism of regular on-line high-flux hemodiafiltration on left ventricular structure and function in maintenance hemodialysis patients. Methods Fifty-three maintenance hemodialysis patients were recruit in this Blood Purification Center, and were randomly assigned to regular hemodialysis (HD) group or regular hemodialysis plus on-line hemodiafiltration (HD+HDF) group. Before and after 6 months of the treatment, the left ventricular structure and function parameters (LVD d, LVVd, E/A, EF and LVMI), the basic condition parameters (MAP, Hb, BMI and Scr), and the HD-associated chronic injury parameters (CRP, IL-1β, β2-MG, and PTH) were determined. Results At the time of recruitment, there were no differences between the two groups in all these parameters. For the patients in HD group after 6 months treatment, there were no significant changes in basic condition parameters, but HD-associated chronic injury parameters became worse. For the patients in HD+HDF group after 6 months treatment, the basic condition parameters of BP and Hb, and all HD-associated chronic injury parameters improved. For patients in both HD and HD+HDF groups, all left ventricular structure and function parameters aggravated, but the degree of aggravation was less in HD+HDF group. Conclusion Regular on-line high-flux hemodiafiltration may alleviate the damage to left ventricular structure and function in maintenance hemodialysis patients.