In the present work the influence of bag materials on the moisture loss and final aflatoxin content of stored moist in‐shell peanuts (MIP) was studied in the rainy season of 1990, in Marília, São Paulo, and in the rainy season of 1991, in Jaboticabal, São Paulo. In each season, MIP were ventilated, as they arrived from the field, to get rid of extraneous materials and then put into 120 bags of jute and into 120 bags of polypropylene, and stored in stacks (12 bags base × 10 bags high). In the rainy season of 1990 (February‐April) moisture and aflatoxin were determined at the beginning (average moisture = 14.31%; aflatoxin not detected). Subsequently, moisture was determined twice a week in samples taken from the external part of the stacks for 80 days, when the stacks were dismantled and moisture and aflatoxin were determined in six samples of each stack. In the rainy season of 1991 (February-March), because of operational difficulties, closed mesh jute bags were used (green coffee type) and the experiment lasted only 30 days. Moisture and aflatoxin were determined only at the beginning (average moisture = 15%; aflatoxin not detected). At the end of the storage period three samples were taken from each lot, for moisture and aflatoxin analyses. The results showed, in both experiments, that in jute bags, even with closed mesh, moisture loss was slightly faster with an average final moisture = 9.68% in jute bags and 10.38% in polypropylene in 1990, and 9.50% in jute and 10.36% in polypropylene in 1991 and that the final aflatoxin content was considerably lower in jute bags, with average figure of 51μg/kg (1990) and 361μg/kg (1991) for jute against 1380μg/kg (1990) and 3703μg/kg (1991) for polypropylene. From the results it was concluded that the use of jute bags for storage of moist in‐shell peanuts allowed a slightly better moisture loss when compared with polypropylene bags and that the use of jute bags showed that this may be better than polypropylene and can be considered for preventing aflatoxin build‐up during storage of in‐shell peanuts, especially when threshed and bagged moist. However, further studies are needed.