Weakness, thin appearance, , high blood pressure, anemia, itches, darkened skin color and nausea are the clinical signs of inadequate hemodialysis. Based on literature reviews, there are 9 factors that directly influence the adequacy of hemodialysis; body mass index (BMI), vascular access, length and frequency of hemodialysis, blood flow rate, ultrafiltration rate, dialyzer surface area, heparinization, and hematocrit. This study aimed to study the dominant predictor of dialysis adequacy in hemodialysis patients in PKU Muhammadiyah Hospital Yogyakarta. Cross sectional study was done involving 90 respondents through purposive sampling method. The hemodialysis adequacy was assessed using the Kt/V formula. All data were collected during the second session of hemodialysis. Data were examined using double linier regression. The ,ean dialysis adequacy was 1.36±0.377. The statistic test result revealed a significant correlation between dialysis adequacy and BMI and the type of heparinization. There was no significant correlation with the type of vascular access, blood flow rate, ultrafiltration rate, hematocrit, length and frequency of hemodialysis, and dialyzer surface area with dialysis adequacy. In conclusion, the dominant factors influencing dialysis adequacy on hemodialysis patients are BMI and type of heparinization.