Background: This study aimed to evaluate the correlation between duplex ultrasonography (DUS) and ultrasound dilution (UD) measurement’s results and determine the factors affecting the correlation of the measured values among other clinical factors in patients. Methods: This cross-sectional study was conducted from April 2020 to May 2020 and included 60 patients who visited our dialysis centre. The flow of the fistula was measured in the proximal brachial artery using DUS. While dialysis was performed on the same day, the access flow was measured using the UD method. The correlation and agreement between the access flows acquired by each measurement method were analysed. Similarly, the correlation was analysed by classifying the groups based on the predisposing factor, and statistically significant factors were observed through comparison. Results: Both measurements showed a moderate positive correlation ( r = 0.60, p < 0.01). The bias (mean of UD-DUS) between the two measurements was about 230 mL/min. When the measurement site of DUS was near the inflow artery and in the same anatomical section, a strong correlation with the measurement value of UD was observed (brachial based fistula: r = 0.85, radial based fistula: r = 0.87). Similarly, for patients without diabetes and those who regularly underwent access surveillance for the dialysis route, strong correlations were observed between the two measurements ( r = 0.79 and r = 0.88). Conclusions: Several factors can influence the correlation between UD and DUS. The findings showed a high correlation for DUS measurement sites within the same anatomical section as the inflow artery, patients without diabetes, and patients undergoing periodic surveillance.