A method of producing a surface-treated carbon black powder dispersion includes subjecting carbon black fine particles having a volume average particle size of 100 nm to 20 μm to wet granulation and drying by heating to obtain granulated carbon black having a hardness of 12 cN or less and a pH of less than 7, grinding the granulated carbon black to obtain a ground product having a volume average particle size of 20 nm to 20 μm, and subjecting the ground product to wet oxidization in an aqueous medium. The resulting surface-treated carbon black powder dispersion exhibits excellent print density, print quality, discharge stability, and storage stability when used as an inkjet printer aqueous black ink.