The present invention relates to thermally and chemically stable quantum dots encapsulated with functional polymeric ligands, a thermally stable quantum dot optical film using the encapsulated quantum dots, and a method for preparing the encapsulated quantum dots. The coating of the surface of the quantum dots with the polymer stabilizes the quantum dots and improves the durability and dispersibility of the quantum dot optical film, achieving markedly improved efficiency of photoluminescent quantum dot devices. Therefore, it is anticipated that the present invention will pave the way for practical use of quantum dots in a variety of light-emitting applications, particularly in high power light-emitting sources, to find commercial application in various fields, including displays, bioimaging, lightings, and photovoltaic cells.