Biodiesel is a clean and cyclical energy resource that is derived from animal and/or vegetable fat. As it blends well with petrodiesel, biodiesel is added to Brazilian commercial diesel. The main raw materials used to produce biodiesel in Brazil include soybean, corn, and sunflower oils. However, these are also used for human consumption and hence, have a high market value. Therefore, pinhão manso oil, which exhibits high productivity at low cost, is a promising alternative. However, the high acidity index of this oil results in a low transesterification yield and the produced biofuel does not meet the requirements imposed by the ANP. Thus, this study intends to demonstrate that a large part of the free fatty acids in pinion oil are present in the seed endocarp. For the development of the project, the oil was extracted by hot solvent, using the soxhlet equipment and the hexane solvent, to determine the acidity index, the titration technique was used, the titrant used was sodium hydroxide. So the acidity index of the oil extracted from the seed with its shell is 10.9 mgKOH/g, while the lipid obtained without the shell exhibits a value of 0.95 mgKOH/g, proving the influence of the endocarp.