This invention provides a method for producing a polymer alloy, a polymer alloy as well as a molded article, a transparent molded article and an optical film, which is obtainable by using the polymer alloy.The invention is a method for producing a polymer alloy, which comprises at least: a step 1 of mixing two or more resins incompatible with each other at ambient temperature and pressure with a solvent being in a liquid or gas state at ambient temperature and pressure; a step 2 of heating and applying pressure to said solvent into a high-temperature and high-pressure fluid or a supercritical fluid and mixing the solvent in this state; and, a step 3 of cooling the mixture obtained in said step 2 rapidly to the glass transition temperature or less without releasing the pressure of the mixture.