Introduction: The use of traditional storage facilities by most of the grain farmers and traders in Nigeria promotes fungal contamination of stored grains and subsequently mycotoxins which are potent carcinogens, neurotoxic, hepatotoxic and immunotoxic when consumed. This study was conducted to determine the incidence and phenotypes of mycotoxigenic fungi associated with commonly consumed food grains in Katsina state, Nigeria. Method: Fungal population in 21 composite samples each of maize, wheat, rice and peanuts from three open markets were determined using standard mycological techniques. Aspergillus spp obtained from the sam- ples were screened for aflatoxigenicity and subsequently characterised by Attenuated Total Reflectance Fourier Transformed Infrared (ATR-FTIR) spectroscopy. Results: A total of 136 filamentous fungi belonging to 19 species were isolated, of which Aspergillus flavus (18.4%), Mucor racemosus (13.2%) and Aspergillus niger (10.3%), were predominant. The highest level of contamination was found in the peanuts (1.8 x 105 ± 2.5 x
105 CFU/g). All the 12 Aspergillus parasiticus and 18 (72%) of Aspergillus flavus isolates obtained from the samples produced aflatoxin B1 on solid media as observed under ultraviolet light and confirmed by Thin Layer Chromatography. The ATR-FTIR spectra of both toxigenic and atoxigenic Aspergillus spp showed similar pattern. Conclusion: The levels of the mycotoxigenic fungi in the food grains, except for rice, were above the permissible limit of 100 to 10,000 CFU/g set by ICMSF, this signifies that they are unsafe for use as food or feed ingredients and hence, the need for more stringent control measures.