A simple, economical, and rapid method to detect aflatoxin in peanut is described in this paper. The extract from 1 g of peanut is added to 1 mL of NH₄H₂PO₄-HgCl₂ solution containing 0.005 g agar in a tube. The concentration of aflatoxin can be visually estimated by the tube fluorescence which is directly correlated with the concentration of aflatoxin on a simple linear regression (r = 0.999, P < 0.01). The lowest aflatoxin amount that could be detected was 0.02 μg/g by a spectroflurophotometer and was 0.04 μg/g by visual observation under UV light. There was no significant difference between the amounts of aflatoxin estimated by the tube fluorescence method and by TLC (P > 0.10) in an experiment containing 10 samples. This method should be applicable for fast identification of peanut genotypes of single plants with resistance to aflatoxin production.