Provided are a composition that contains a quantum dot fluorescent body and that is able to suppress quenching of the quantum dot fluorescent body, a molded body of a quantum dot fluorescent body dispersion resin, a structure containing a quantum dot fluorescent body, a light-emitting device, an electronic apparatus, or a mechanical device, and a method for producing the molded body of a quantum dot fluorescent body dispersion resin. A quantum dot fluorescent body is dispersed in a cycloolefin (co)polymer that is a dispersion resin to form the composition containing a quantum dot fluorescent body, and the composition containing a quantum dot fluorescent body is molded, forming the molded body of the quantum dot fluorescent body dispersion resin, and a gas barrier layer that reduces the passage of oxygen to the molded body of the quantum dot dispersion resin is formed at a portion or the entirety of the surface of the molded body of the quantum dot fluorescent body dispersion resin, and furthermore, a light-emitting device is configured using the composition containing the quantum dot fluorescent body as a sealing material that seals an LED chip.