The production of biodiesel from chicken fat and pennycress oil through esterification and transesterification processes using sulfuric acid (H2SO4) as the acid catalyst and different concentrations of potassium hydroxide (KOH) as the basic catalyst was evaluated. This study quantified the effects of the concentration of basic catalyst on the percent of fat conversion and on the yield of biodiesel. The biodiesel was evaluated for its properties as a fuel and compared with the standards of the American Society for Testing and Materials (ASTM) for biodiesel based on its viscosity, flash point, cloud point, and total glycerin by gas chromatography. The results indicated that a concentration of 1.0% KOH at 60°C, with 60 minutes of reaction time and a 6:1 molar ratio of alcohol-oil resulted in the best yield (81.91%) from chicken fat with the highest conversion percentage (96.5%). The yield of biodiesel from pennycress oil was lower (77.44%) than that from chicken fat. The biodiesel obtained under these conditions had characteristics very similar to those described in the ASTM standards for biodiesel.