A label-free method was developed for the detection of kanamycin using gold nanoparticles(GNPs).This method was based on the fact that aptamer can make GNPs maintain monodispersed in NaCl solution and keep red color.After adding kanamycin into the solution,due to the specific interaction of aptamers with kanamycin,the stability of GNPs was reduced as the aptamer was firstly interacted with kanamycin and removed from GNPs,which induced GNPs aggregating in the presence of NaCl,and the color of the solution was changed into blue or blue-violet,correspondingly.According to the absorbance change of the solution at 630 nm,the content of kanamycin could be rapidly detected using a simple microplate reader with fixed wavelength.The linear range of kanamycin was in the range of 1-10 nmol/L,with a detection limit of 1 nmol/L.The detection process could be accomplished in 5 min.This method could be used to detect kanamycin in milk samples,with advantages of good selectivity and high sensitivity,and is of great significance to detect the excessive antibiotics addition in food.