Composition of photostable sunscreen in a microemulsion format with dispersed phase drops in the size range of 4 to 100 nm, the composition of the photostable sunscreen comprising: 0.1% to 10% by weight of dibenzoylmethane or its derivative, 10 to 40% by weight of an emulsifier, 5 to 40% by weight of a coemulsifier selected from the group consisting of C2 to C8 straight or branched chain alcohol, polyhydric alcohol and C5 to C8 low molecular weight fatty acid, 10 to 50% by weight of a hydrophobic liquid having a log P value at 25 degrees Celsius greater than 3 and a water solubility at 25 degrees Celsius less than 0.1% by weight, and 10 to 50% in water weight； wherein said emulsifier is a non-ionic surfactant； wherein the benzoylmethane derivative is selected from 4-tert-butyl-4'-methoxydibenzoylmethane, 2- methyldibenzoylmethane, 4-methyl-dibenzoyl methane, 4-isopropyldibenzoyl methane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane , 2,5-dimethyldibenzoylmethane, 4,4'-diisopropyl-dibenzoylmethane, 2-methyl-5-isopropyl-4'-methoxydibenzoylmethane, 2-methyl-5-tert-butyl-4-methoxy-dibenzoylmethane, 2,4-dimethyl -4'-methoxy-dibenzoylmethane or 2,6-dimethyl-4-tert-butyl-4'-methoxy-dibenzoylmethane.Composición de filtro solar fotoestable en un formato de microemulsión con gotas de fase dispersa en el intervalo de tamaño de 4 a 100 nm, comprendiendo la composición de filtro solar fotoestable: del 0,1% al 10% en peso de dibenzoilmetano o su derivado, del 10 al 40% en peso de un emulsionante, del 5 al 40% en peso de un coemulsionante seleccionado del grupo que consiste en alcohol de cadena lineal o ramificada C2 a C8, alcohol polihidroxilado y ácido graso de bajo peso molecular C5 a C8, del 10 al 50% en peso de un líquido hidrófobo que tiene un valor de log P a 25 grados centígrados mayor de 3 y una solubilidad en agua a 25 grados centígrados menor del 0,1% en peso, y del 10 al 50% en peso de agua； en la que dicho emulsionante es un surfactante no iónico； en la
