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Magnetic petrological investigations were conducted on the pumice fall deposits of the 1783 eruption of Asama volcano to examine relationships between bulk magnetic properties and petrological features related to the magmatic and volcanic processes of the eruption. The magnetic properties of the deposits agree with the mineralogical investigation, indicating the existence of titanomagnetite and pyrrhotite as magnetic minerals in the deposits. Although most magnetic properties are common over depositional units, mass-specific magnetic susceptibility decreases as the eruption progressed, implying a change in titanomagnetite abundance. This is consistent with a previously proposed binary magma mixing model and is because of the increasing mafic endmember component without titanomagnetite. Our results demonstrate that magnetic petrology can be a useful tool for investigating volcanic and magmatic processes. [ABSTRACT FROM AUTHOR]