Natural fibers have attracted much attention due to their applications as reinforcements in thermoplastic and biodegradable polymers, and improvements in the mechanical and barrier properties of the biofilms. In literature it is reported that the addition of cellulose fibers considerably increased the tensile strength and Young modulus of the films, and reduced their elongation capacity. Nanofibers may have properties similar to traditional fibers. In this context, the objective of this study was to incorporate bacterial cellulose nanofibers in starch acetate films and characterize those films by mechanical and barrier properties. The films were obtained from suspensions prepared with 3 g of starch acetate (produced in laboratory), 100 g distilled water, glycerol (0.30 g.g-1 starch acetate), guar gum (0.06 g.g-1 starch acetate) and bacterial cellulose fibers (0.025, 0.075 e 0.125 g.g-1 starch acetate), dispersed in a mechanical shaker, heated to 85°C and stirred for 30 min to dissolve the starch acetate. While still heated, the suspensions were spread on acrylic plates and dried at 35 °C for 7 h in a forced air circulation oven until the moisture equilibrium was reached (11. 5 ± 0.8 %) ("casting" method). After drying, samples were cut from the films and conditioned at 58 %, for 4 d, before testing. Starch acetate films were used as control. The results of tensile trials showed that the acetylated films with addition of bacterial cellulose increased 2, 3 and 7 times the values of stress at break and 2, 3 and 11 times, approximately, the values of Young modulus when comparing to the results of the control films. These results indicated that the addition of nanofibers is an alternative to improve the mechanical resistance of the films. The reductions in the values of hygroscopicity were small.