The utilization of liquid fuels such as biodiesel produced from used frying oil by transesterification process and it represents one of the most promising optional sources to replace the use of conventional fossil fuels. This study used two kinds of UFPO (palm oil), UFGO (groundnut oil) to characterization and optimization the biodiesel. The process variables are : methanol to oil molar ratio (3 : 1-12 : 1); catalysts (KOH, NaOH, CH3OK and CH3ONa); catalyst concentration (0.5, 1.0, 1.5 and 2.0 wt%); temperature (50, 55, 60 and 65 degrees C); time (30, 60, 90 and 120 min) and methanol used this experiment. In that, UFPO shows higher biodiesel yield than UFGO and the optimized biodiesel parameters were : KOH catalyst, 6 : 1 molar ratio, 1.0 wt% of catalyst concentration, 60 degrees C temperature, and 120 min reaction time. FTIR technique is used to identify the peaks formed in final biodiesel product in UFPO. These optimized biodiesel parameters are meets the quality specifications required by the European Standard for biodiesel, i.e. EN 14214 : 2010 and also Biodiesel were confirmed by FTIR technique.