Cereal-based products have become an excellent vehicle for delivering tasty functional food ingredients to busy consumers. One emerging trends is food products formulates with soy protein because of its proven health benefits. Because of the potential usefulness of these products, it was considered of interest to determine the stability of cereal bars based on soy protein, wheat germ and oat, enriched with vitamin C (ascorbic acid) and E (acetate of a-tocopherol 50%), during the storage. Three films with different properties of barrier (A: PET/PEBD; B: PETMET/PEBD; C: PET/PEBD/ALIPEBD) were used as packing and the cereal bars were stored at temperature (25 +/- 2 degrees C) and relative humidity ambient (56%) for six months. The stability of vitamin C, vitamin E and, its lipase and peroxidase activity was verified. During the study, the cereal bars packed in three tested films presented retention in the vitamin C lesser that 50%. However, packing structuralized with aluminum (C) leaf provided to minor speed of reaction during the storage, k = 0.00437 (-day), and greater time of half-life (146 days). The vitamin E (acetate of a-tocopherol) in the cereal bars presented a little variation during the storage. It had a significant (p < or = 0.05) increase in the peroxidase activity at 90 days of storage in the packages tested, while that the lipase activity demonstrated no significant increase during the period studied.