Provided is a molecular assembly (for example, a polymeric micelle nanoparticle) which is capable of efficiently containing a fat-soluble medicinal agent. A molecular assembly which contains: an amphiphilic block polymer A1 which comprises a hydrophilic block having a sarcosine unit and a hydrophobic block having a lactic acid unit a hydrophobic polymer A2 having a lactic acid unit a fatty acid triglyceride and a fat-soluble medicinal agent. Examples of the fat-soluble medicinal agent include miriplatin.本發明提供一種可效率良好地內包脂溶性藥劑的分子集合體(例如,高分子膠束奈米粒子)。一種分子集合體,其包含:兩親性嵌段高分子A1,具有含有肌胺酸單元的親水性嵌段與含有乳酸單元的疏水性嵌段;具有乳酸單元的疏水性高分子A2;脂肪酸三酸甘油酯;及脂溶性藥劑。作為脂溶性藥劑的例子,可列舉米鉑。
