Provided are: a heat-conductive filler which is characterized by comprising particles which are produced by coating magnesium oxide with magnesium carbonate; a method for producing a heat-conductive filler, which is characterized by comprising the steps of injecting a carbon dioxide gas into a slurry that is prepared by dispersing magnesium oxide particles in water and then performing a hydrothermal treatment while dissolving carbon dioxide in water; a resin composition prepared using the heat-conducive filler; and a molded product of the resin composition. The heat-conductive filler, the resin composition, the molded product of the resin composition, and a highly heat-conductive material produced using the molded article have excellent heat conductivity and wet heat resistance.
