An inkjet aqueous pigment dispersion which achieves high pigment concentration, exhibits favorable redispersion properties after drying, and does not exhibit changes in ink properties even when stored for a long time; and an ink composition using the aqueous pigment dispersion. The inkjet aqueous pigment dispersion contains a pigment, a liquid medium, and a polymer dispersion agent which is an A-B block polymer obtained by copolymerization using a mixture of an organic tellurium compound represented by formula (1) and an organic ditellurium compound represented by formula (2) as a polymerization initiator. The monomer for configuring the A block is at least one type of monomer represented by formula (3), and the monomer for configuring the B block is benzyl methacrylate and/or benzyl acrylate.