Abstract: A safe medical powder with excellent performances which is a magnetosensitive powder for diagnosis, therapy, or drug delivery and which, even when placed in the body for a prolonged period, neither suffers a decrease in magnetic sensitivity nor releases ions, etc. The medical powder comprises a base particle of a ferromagnetic metal having thereon a coating layer, wherein at least the outside of the coating layer comprises a bioinert substance. Preferably, the coating layer comprising a bioinert substance comprises a layer comprises a hydrolysate of an alkoxide compound.