In this research, the influence of the percentage by weight of cellulose and glycerin on the tensile strength, strain and stiffness of biofilms based on modified starch from the seed of Persea amerinaca Mill (avocado seed) was evaluated. Starch and cellulose were extracted by wet method and treatments (alkaline and acid) respectively. Biofilms were obtained by the solution fusion method. The percentages by weight of cellulose, as reinforcement, were 45, 50 and 55%; and glycerin, as a plasticizer, were 20, 25 and 30%; these dosages were used in the preparation of biofilms. For the tensile test, the guidelines of the ASTM D882- 12 standard were followed. The biofilms reached maximum tensile strength and stiffness values of 12.10 MPa and 54.05 MPa respectively; when the films were reinforced with 55% cellulose and plasticized with 20% glycerin; On the other hand, minimum tensile strength va...