Aflatoxin B1 (AFB1) is a fungal toxin common in crops and it is the most toxic of all mycotoxins which can cause cancer. Thus, quick and effective detection of AFB1 is important for food security. Here, a simple and sensitive optical sensor based on surface-enhanced fluorescence (SEF) technique was designed to detect AFB1. We used nanoporous gold (NPG) as the substrate. The AFB1 aptamer (Cy5-DNA1) and AFB1 complementary aptamer (SH-DNA2) were successively assembled on the surface of NPG to form the optical sensor for AFB1. Competitive binding between AFB1 and Cy5-DNA1 released Cy5-DNA1 from NPG, leading fluorescence intensity of Cy5 to fall. AFB1 was detected by monitoring the variation of the fluorescnece intensity of Cy5 and the final detection limit was 10^-7μg/L with a linear dynamic range 4 orders of magnitude.