Citric acid production in solid-state fermentation by Aspergillus foetidus ACM3996 was better on pineapple waste than on apple pomace, wheat bran or rice bran, The highest citric acid content achieved on pineapple waste was 16.1 g per 100 g dried pineapple waste, with a moisture content of 70% and in the presence of 3% methanol. This represents a yield of 62.4% based on the sugar consumed.