There are provided a carbon black according to which long-term stable storage is possible, clogging is not prone to occurring, and the OD value is high and hence printing with a deep black color is possible, or a carbon black that can be used in a water-based ink that is used in ink jet printer printing, that has low settleability and can thus be stored stably for a long period, for which clogging is not prone to occurring, and for which the reflection density is high and hence printing with a high printing density and a deep black color is possible, a carbon black dispersion having the carbon black dispersed therein, and a water-based ink containing the carbon black. An embodiment of a modified carbon black of the present invention is a modified carbon black obtained by carrying out oxidation treatment on a carbon black having a primary particle diameter of 11 to 18 nm, a BET specific surface area of at least 180 m.sup.2/g, a DBP oil absorption of at least 180 mL/100 g, and a value of the BET specific surface area (m.sup.2/g) divided by the DBP oil absorption (mL/100 g) of 0.75 to 1.3, and is characterized in that at least lactone groups and carboxyl groups are introduced onto the surface thereof, and the ratio of the mean particle diameter to the primary particle diameter is at least 8.5. Moreover, a carbon black dispersion and a water-based ink of the present invention contain this modified carbon black.