To overcome the problem of aflatoxins (AF) in Thai foods, a sensitive in-house direct cELISA using monoclonal antibody (mAb) was established and compared with a commercial ELISA kit and thin-layer chromatography for the determination of AFB1 levels in corn and peanuts. Among eight in-house mAbs (AF1-8), AF5 was used in the direct cELISA owing to its excellent specificity and sensitivity with the detection limit of 4 μg kg-1. The recovery of AFB1 spiked at 5, 10, 20, 40 and 80 μg kg-1 ranged from 88.1 to 99.5 %. Correlation coefficients of the ELISA with the commercial ELISA kit and thin-layer chromatography were 0.912 and 0.802 for corn, and 0.941 and 0.832 for peanuts, respectively (p < 0.05). The cost per sample was estimated to be about 16 times lower than the commercial ELISA kit. Subsequently, the in-house direct cELISA was successfully applied to screen the contamination of AFB1 in Thai corn and peanuts. Mean levels of AFB1 (per cent positive were 73 μg kg-1 (85.7%) in corn and 102 μg kg-1 (67.9%) in peanuts, for which 46.4% of both foods were above the Thailand regulation limit (20 μg kg-1).