A dispersion comprising quaternary ammonium ions (A) each having a total carbon atom number of 15 to 45 and one or two C10-20 alkyl groups, and an anionic surfactant (B) having an ammonium ion, wherein plate-like particles (C) having an average thickness of 0.7 to 40 nm, an average major-axis length of 100 to 600 nm, an average minor-axis length of 50 to 300 nm, and a ratio of average major-axis length to average minor-axis length of 1.0 to 10.0 are dispersed in a liquid medium, and the plate-like particles (C) in the dispersion have an average particle diameter of 10 to 600 nm as measured by dynamic light scattering.