Crystallization of uracil (URA) induced by the imprinting effect is observed when a poly(acrylonitrile-co-methacrylic acid) membrane has been prepared in supercritical CO2 using phase-inversion imprinting technology. The URA-imprinted membrane forms flower-like crystals of URA on the surface, but neither a non-imprinted membrane nor the membrane left in the LIRA aqueous solution shows crystal formation. Effects of organic solvents on the URA-imprinted membrane tire examined for the membrane was prepared in supercritical CO, fluid. Evidence shows that supercritical CO2 media is important for the formation or URA crystals on the imprinted membrane.