Aflatoxins are toxic, carcinogenic fungal metabolites that could occur as contaminant in food and feed worldwide. Health concerns and regulations that limit the use of contaminated commodities greatly influence the profitability of several crops in Thailand including corn and peanut. Soil samples from corn producing regions in north of Thailand were plated in aspergillus flavus and parasiticus agar (AFPA) in order to screen for Aspergillus spp. Predominant genera were found to be Aspergillus flavus,  A. parasiticus and Penicillium spp. Most A. flavus and A. parasiticus were toxigenic and produced aflatoxin B1 (AFB₁) at 30^OC within 10 days in AFPA. Some of the isolates of Aspergilli, including A. flavus, A. carbonarius, A. oryzae, A. niger and A. terreus showed cellulolytic activities in carboxymethylcellulose agar (CMC agar).