The objective of this study was to develop a new method for measuring polyvinylpyrrolidone (PVP) eluted from polysulfone (PSu) membrane dialyzers. The Müller method is generally used for the measurement of PVP, in which the PVP concentration is determined by measuring the absorbance after a red color is generated by the formation of PVP-iodine complexes when iodine is added to a sample. In contrast, our method does not require any reagents and allows real-time measurement of PVP by the ultraviolet absorption spectrum (UV-s method). In this study, the UV-s method and the Müller method were used to measure PVP eluted from two types of PSu membrane dialyzer (PS-1.6UW sterilized by autoclaving [n = 10] and APS-15SA sterilized by gamma radiation [n = 10]). Polyvinylpyrrolidone concentrations measured by the two methods showed a significant positive correlation (rs = 0.99, p = 0.0006). The PVP concentration (median [25th-75th percentiles]) in PS-1.6UW dialyzer washings obtained by rinsing with physiologic saline was 2.0 (1.18-4.85) mg/L with the Müller method and 3.35 (2.38-4.23) mg/L with the UV-s method, showing no significant difference. However, the PVP concentration in APS-15SA dialyzer washings was 0 (0-0.35) mg/L by the Müller method and 0.95 (0.45-2.58) mg/L by the UV-s method, and there was a significant difference between the two methods. In conclusion, the low concentration of PVP eluted from a PSu dialyzer sterilized by gamma radiation was hardly detected by the Müller method but could be clearly detected by the new UV-s method. These findings suggest that the UV-s method could be used for real-time measurement of PVP eluted from PSu membrane dialyzers.