Background Chronic inflammation as a major determinant of ‘dialysis syndrome’ is considered as the main factor of morbidity and mortality in dialysis patients. Tumor necrosis factor-alpha (TNF-α) may play important roles in the development of T helper (Th) imbalance, cardiovascular disease, and wasting in the uremic milieu. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide that may be an independent risk factor for endothelial dysfunction and cardiovascular disease. In hemodialysis (HD) patients, plasma ADMA is a strong and independent predictor of overall mortality and cardiovascular outcome. The aim of this study to evaluate the acute effects of hemodiafiltration (HDF) compared with conventional HD on blood levels of ADMA and TNF-α. Patients and methods A cross-sectional study was conducted on 20 patients with end-stage renal disease receiving dialysis in the dialysis unit of Ain Shams Specialized Hospital receiving twice weekly HD session with high-flux (HF) dialyzer and once weekly HDF session. Blood samples were collected from all participants before and after HD session and from the same participants before and after HDF session. ADMA and TNF-α levels were assessed by enzyme-linked immunosorbent assay techniques. Results The decrease in TNF-α was higher after HDF session versus HF HD session (79.47 ± 14.16 vs. 50.43 ± 31.05), with P value of 0.001. Moreover, the decrease in ADMA was higher after HDF session versus HF HD session (75.01 ± 12.55 vs. 41.79 ± 24.73), with P value of 0.001. Conclusion The use of online HDF technique showed a significant reduction of ADMA and TNF-α in adults with end-stage renal disease.