Objective To investigate the feasibility and accuracy of online clearance mornitoring(OCM)in assessing hemodialysis adequancy by a prospective auto-control study. Methods Sixty patients with maintenance hemodialysis were investigated on OCM appliance,whose average hemodialysis duration were (86±23) ms,blood flow was 220～300ml/min,dialysate flow was 500ml/min.Meanwhile,blood urea nitrogen(BUN) of pre-and post-dialysis were examined.Then caculate Kt/V according to the equation Daugirdas and evaluate the correlation between Kt/V by OCM and by calculation.Kt/V by OCM and by calculation were also compared in different body surface area and ultrafiltration volume. Results Kt/V by OCM and by calculation was (1.50±0.18)vs(1.62±0.48) respectively, γ,the correlation coefficient of linear regression analysis,was 0.747(P＜0.001).In group A(body surface area ≥1.73m2) and group B(body surface area＜1.73m2), the Kt/V by OCM was (1.28±0.07) vs (1.67±0.45) respectively,the difference between them was significant; the Kt/V by calculation was (1.47±0.15) vs (1.52±0.19) respectively, there was no significant difference between them.And there was no significant difference in Kt/V in the group with ultrafiltration volume ≥3Kg and the group ＜3Kg. Conclusion Correlation between Kt/V by OCM and by calculation was satisfactory. The operation of OCM was convenient and can guarantee hemodialysis adequacy. OCM could be applied in clinic widely.