PROBLEM TO BE SOLVED: To provide nanoparticles having a particle size suitable for filtration sterilization and suitable for application to drug delivery system nanoparticles. SOLUTION: A poorly water-soluble physiologically active compound and an additive substance are contained at least, and Reactive Span Factor (RSF) satisfies the following formula, 0 <；(RSF) ≤ 1.0. The nanoparticles have an average volume reference particle diameter of 200 nm or less, and the poorly water-soluble physiologically active compound is coated with the additive substance. The embodiment in which the average volume reference particle diameter is 5 nm or more and 150 nm or less is preferable, and the embodiment in which (RSF) satisfies 0 <；(RSF) ≦ 0.6 is more preferable. [Selection diagram] None【課題】ろ過滅菌に適し、ドラッグデリバリーシステムナノ粒子に適用するのに最適な粒子径を有するナノ粒子の提供。【解決手段】難水溶性生理活性化合物と、添加物質とを少なくとも含有し、Ｒｅｌａｔｉｖｅ Ｓｐａｎ Ｆａｃｔｏｒ（Ｒ．Ｓ．Ｆ）が次式、０＜（Ｒ．Ｓ．Ｆ）≦１．０、を充たし、平均体積基準粒子径が２００ｎｍ以下であり、前記難水溶性生理活性化合物が、前記添加物質により被覆されているナノ粒子である。前記平均体積基準粒子径が５ｎｍ以上１５０ｎｍ以下である態様が好ましく、前記（Ｒ．Ｓ．Ｆ）が、０＜（Ｒ．Ｓ．Ｆ）≦０．６、を充たす態様がより好ましい。【選択図】なし
