Biodiesel is an alternative fuel that is more environmentally friendly and renewable. Biodiesel can be categorized as bioenergy or vegetable fuel, because it is made from vegetable oil. In this research, biodiesel is produced from the process of transesterification of used cooking oil. The purpose of this study was to determine the effect of variations in the weight variables of anhydrous Na2SO4, duration of contact time, and speed of stirring to the purity of biodiesel produced, and determine whether the results of biodiesel washed with anhydrous Na2SO4 according to ASTM standards or not. From the research conducted, the results of making biodiesel from used cooking oil are only through the transesterification stage and without the esterification stage, because the FFA value is less than 2%, which is 0.4 mgKOH / g. Washing biodiesel with anhydrous sodium sulfate (Na2SO4) adsorbent can be used as an alternative biodiesel washing agent from used cooking oil. The research shows that the variation of variables that produce the most optimum value and meets 5 parameters of SNI 7182: 2015 / ASTM Biodiesel test is the variation of anhydrous sodium sulfate (Na2SO4) adsorbent used as much as 3% of the volume, reaction time for 30 minutes, and stirring speed of
150 rpm. From the variation of variable result the number of flash point is
132,33 oC, viscosity 4,9 cSt, density 854,66 kg/m3, water content 0,040 %V, dan cetane number is 47,66.