Acid number is an important quality parameter for biodiesel and biodiesel blends and has been included in various quality standards including ASTM D 6751 and EN 14214. In this paper, a new simple and green potentiometric method based on green chemistry approaches has been developed to determine the acid number of biodiesel and biodiesel blends. This new method uses a reduced amount of titration solvent and recommends the use of a small sample size instead of large sample size as stated in the ASTM reference method D664. A time-efficient electrode cleaning procedure has been developed which completely eliminates the use of toxic solvents for cleaning the electrodes. This proposed green method significantly reduced the maximum % error from 101% to only -18% and repeatability was decreased from 290% to 100% when compared to ASTM D 664 method using the sample size of 2 g. This proposed green analytical method could be used for the determination of acid number of biodiesel and biodiesel blends in R&D as well as in industrial quality control laboratories as a simple, time-efficient, cost effective, and environmentally friendly method for acid number determination. (c) 2012 Elsevier Ltd. All rights reserved.