PROBLEM TO BE SOLVED: To reliably provide a cured product which is a composite material in which inorganic particles are dispersed in a resin matrix and which can develop a structural color having a constant color tone which is not influenced by a change in incident angle of light. Provided is a method for producing a polymerization-curable composition having excellent inorganic particle dispersibility. SOLUTION: The polymerizable monomer serving as a matrix resin and an inorganic having a specific average primary particle diameter, an extremely narrow particle size distribution width, and a refractive index larger than that of a cured body of the polymerizable monomer. When producing a polymerization-curable composition by mixing with spherical particles, for example, the radial distribution function of the cured product is evaluated by appropriately sampling in the mixing step, and finally, the distance between the closest particles is inorganic. The particles are mixed so that the average particle diameter of the spherical particles is 1 time or more and 2 times or less, and the minimum value between the closest interparticle distance and the next adjacent interparticle distance is 0.56 or more and 1.10. [Selection diagram] Figure 1【課題】 樹脂マトリックス中に無機粒子が分散してなり、光の入射角の変化に左右されない一定の色調の構造色を発色することができる複合材料となる硬化体を確実に与えることができるような無機粒子分散性を持った重合硬化性組成物を製造する方法を提供する。【解決手段】 マトリックス樹脂となる重合性単量体と、特定の平均一次粒子径を有し、粒度分布幅が極めて狭く、且つ前記重合性単量体の硬化体よりも大きな屈折率を有する無機球状粒子とを混合して重合硬化性組成物を製造するに際し、たとえば混合工程中で適宜サンプリングを行ってその硬化体の動径分布関数を評価し、最終的に、最近接粒子間距離が無機球状粒子の平均粒子径の１倍以上２倍以下となり、且つ、最近接粒子間距離と次近接粒子間距離との間における極小値が０．５６以上１．１０以下となるように混合する。【選択図】図１
