A reversible, conventional, and rapid purification method of hydrophobically tagged products Using hydrophobic magnetic nanoparticles was developed. The reversible purification system entails simply controlling the polarity of solvents. First, for the catching procedure, poor solvents were added into a well-dispersed system of magnetic nanoparticles and tagged products. Once the poor solvents were added to the system, the products were recrystallized among the nanoparticles and the aggregation of magnetic nanoparticles occurred due to hydrophobic interactions. These aggregates with the products contained within them were able to be collected rapidly by magnets, Then, the releasing procedure can be easily performed by redispersing the collected aggregates into good solvents. The availability of this purification protocol was confirmed by using a hydrophobically tagged fluorescent model product. Furthermore. this rapid purification method was successfully applied to a peptide elongation reaction system which enabled the synthesis of peptides such as Leu-Enkephalin in high purity. in high yield, and in a short time.