Although widely applied in many industries, anionic surfactants (AS) have been shown to contaminate the natural environment. Therefore, the detection of trace amounts of AS in environmental samples is of great interest. Here, we report a novel fluorescence quenching method for the determination of trace AS, specifically, sodium dodecyl sulfate (SDS), using 1-(5-naphthol-7-sulfonic acid) -3-(4-pheny-lazophenyl)-triazene (NASAPAPT). Under optimum conditions, the degree of fluorescence quenching is linearly proportional to the concentration of SDS from 2.08×10-8 to 8.67×10-7mol L-1 with a detection limit of 8.35×10-9mol L-1. The proposed method exhibits high sensitivity and selectivity, yet it avoids the use of toxic organic solvents and tedious solvent extraction procedures. It has been applied to the determination of trace SDS in both natural water and industrial samples with recoveries between 99.04 and 103.58%. Results indicated that the hydrogen bonds formed between NASAPAPT and SDS played an important role in the detection process and that the π→π* transition was crucial for fluorescence of the NASAPAPT complex.