The biodiesel used in this study is biodiesel derived from waste cooking oil. The biodiesel synthesis process used esterification and transesterification reactions. This biodiesel has been mixed with diesel with a content of 20, which is called 20 Biodiesel (B20). Lemongrass essential oil was mixed with B20 using a magnetic stirrer for 30 minutes and sonicated for 2 minutes. The tests carried out in this study were chemical characterization and fuel properties. Chemical characterizations include functional group test (FTIR) and fatty acid content (GC-MS). Meanwhile, the fuel properties include density, viscosity, flash point, and low heating value (LHV) tests. The variation of the volume fraction of lemongrass essential oil added to B20 is 0; 0.1; 0.15 and 0.2. The results showed that the methyl ester content in waste cooking oil biodiesel was 96.5 by the requirements for fuel characteristics determined by the Indonesian government. According to ASTM standards, the content of B20 with lemongrass essential oil bioadditive of 0.2 indicates the best fuel properties. © 2023 American Institute of Physics Inc.. All rights reserved.