Disclosed herein are methods and kits for isolating exosomes in a sample. The method comprises contacting and incubating a plurality of galectin-3-modified magnetic beads with the sample, followed by subjecting the mixture to a magnetic field and then isolating the exosomes from the magnetic beads by a lactose solution. The kit of the present disclosure comprises a plurality galectin-3-modified magnetic beads, a lactose solution having a pH value of 6.8 to 7.6, and an exosome-free buffer.