Provided is a molecular assembly having any nano-sized particle diameter depending on its intended use and application, in various fields such as pharmaceutical drugs, agricultural chemicals, cosmetics, food products, and electronics. Furthermore, provided is a nano-carrier for delivering various substances using the molecular assembly having any nano-sized particle diameter. A molecular assembly comprising: an amphiphilic block polymer A1 comprising a hydrophilic block having a sarcosine unit and a hydrophobic block having a lactic acid unit and an amorphous hydrophobic polymer A2 having an aliphatic hydroxy acid unit, wherein a number of aliphatic hydroxy acid units contained in the amorphous hydrophobic polymer A2 exceeds twice a number of lactic acid units contained in the hydrophobic block of the amphiphilic block polymer A1.
