Nano-size cores of Fe3O4 with the strongest magnetism were prepared with a proper feeding ratio of Fe^2^+/Fe^3^+ and a suitable concentration of NaOH solution. Then solid acid ZrO2 was deposited over the magnetic cores to form a novel magnetic nano-size solid acid catalyst: ZrO2/Fe3O4. The new catalysts were characterized by techniques such as XRD, XPS, TEM and by the measurements of specific surface area as well as magnetic properties, etc. They showed high catalytic activities for esterification of acetic acid with butyric mellow. The new catalysts can easily be separated from the reaction system by magnetism.

Key words: NANOPHASE MATERIALS, SOLID ACID, CATALYST, IRON OXIDE, ZIRCONIUM OXIDE, MAGNETISM, ESTERIFICATION, CATALYTIC ACTIVITY