an object of the present invention is to efficiently extract proteoglycan from aquatic animal tissues . the method of the present invention is a method for extracting proteoglycan from fish cartilage , comprising the step of heating small pieces of frozen fish cartilage in water . this method of the present invention enables easy extraction of proteoglycan from fish cartilage with very high efficiency . in particular , the method of the present invention enables extraction of high - molecular - weight proteoglycan . further , since in the method of the present invention , extraction is performed using only water , it ensures safety in the extraction and safety of the resulting proteoglycan product , compared with hitherto known extraction methods using organic solvents or acids / alkali . furthermore , the cumbersome step of removing organic solvents is not necessary in the method of the present invention .