The present invention provides a material that has a good compatibility with monomers and can be used as dispersing agent even after a period of not shorter than one week since the preparation of the dispersion. The dispersion of the present invention comprising metal oxide particles with an average primary particle diameter of not more than 50 nm; an organic acid; a dispersion medium; and an organophosphorus compound represented by formula (1) or an organosulfur compound represented by formula (2).