PROBLEM TO BE SOLVED: To provide a method for producing an ultraviolet protective agent composition having high transparency and excellent in the ability to protect light rays at a wavelength of 200 to 420 nm, which is an ultraviolet region； and an ultraviolet protective composition obtained by the method.SOLUTION: According to the present invention, a method for producing an ultraviolet protective agent composition comprises: (a) mixing, by a micro-reactor, an iron oxide raw material fluid containing at least Feions and an iron oxide precipitation fluid containing at least a basic substance to precipitate fine particles of iron oxide； and (b) dispersing the precipitated fine particles of iron oxide into a dispersion medium to obtain a dispersion of iron oxide fine particles. Here, the dispersion of iron oxide fine particles has a haze value of 2.0% or less, and a light transmittance of 2.0% or less at a wavelength of 200 to 420 nm.SELECTED DRAWING: Figure 3【課題】透明性が高く、且つ紫外線領域である波長２００～４２０ｎｍの光線の防御能に優れる紫外線防御剤組成物の製造方法及び同製造方法によって得られた紫外線防御剤組成物を提供することを課題とする。【解決手段】少なくともＦｅ３＋イオンを含む酸化鉄原料流体と、少なくとも塩基性物質を含む酸化鉄析出流体とをマイクロリアクターを用いて混合させて酸化鉄の微粒子を析出させる工程（ａ）と、上記析出させた酸化の鉄微粒子を分散媒に分散させて酸化鉄微粒子分散体を得る工程（ｂ）とを少なくとも含む紫外線防御剤組成物の製造方法であり、上記酸化鉄微粒子分散体のヘーズ値が２．０％以下であり、かつ上記酸化鉄微粒子分散体の波長２００～４２０ｎｍにおける光線の透過率が２．０％以下である。【選択図】図３
