Biodiesel is the newest attraction to substitute the diesel fuel due to its environmental benefits, but also for being a renewable and sustainable source of energy. This fuel can be produced using vegetable oils or animal fat. Acid oils have become a new raw material for biodiesel production due to the low cost associate with them. However, the amount of free fatty acid contains in this raw material exceed the maximum allow to us conventional homogeneous basic technology. Because of this, a heterogeneous catalyst can be used to perform the esterification reaction of the free fatty acid as well as the transesterification of the triglycerides. In this work, different variable of the process such as the reaction temperature, the amount of catalyst, the molar ratio of alcohol/oil and the initial quantity of free fatty acid was studied with good results. Both reactions were carried on a batch reactor and the conversion was determinate using gas chromatography and titration as wells. For this study a solid resins was used as catalyst, ethanol (anhydride) and a mix of sunflower oils (90% w/w) and oleic acid (10% w/w), were used as raw material From the conversion of free fatty acid it has been determinate that over 80% of them were esterifies into fatty acid ethyl esters and good result were achieved for the transesterification reaction.