To provide a means capable of suppressing the generation of gelation at the time of or after the addition of a silane coupling agent in the production of a cationically modified silica including modifying a silica raw material with a silane coupling agent. The present invention is a method for producing a cationically modified silica, including: mixing a silica raw material having a negative zeta potential with a silane coupling agent having an amino group or a quaternary cationic group; and reacting the silica raw material with the silane coupling agent to obtain a cationically modified silica, in which the cationically modified silica satisfies the following relational expression (1): X