Provided is a method for synthesizing group II-VI compound semiconductor polycrystals in which synthesis can be accomplished without the use of a quart ampoule as the polycrystal synthesis vessel, and as a result it is possible to use a larger vessel without reducing yield, and costs can thereby be reduced. Two or more starting elements are introduced to a semi-airtight pBN inner vessel (6a), the inner vessel is introduced to a semi-airtight heat-resistant outer vessel (6b) and placed in a high-pressure furnace (1) having a heating means (7), the air inside the high-pressure furnace is evacuated and the furnace is filled with an inert gas under a predetermined pressure, the outer vessel and inner vessel are heated and the temperature is raised using the heating means, the starting elements inside the inner vessel are melted and reacted, and the temperature is then gradually lowered to promote growth of polycrystals.