Provided is a sealing member for preventing leakage of a developer from a developer containing portion of a process cartridge detachable from a main body of an electrophotographic image forming apparatus to an outside of the developer containing portion. The sealing member is made of a thermoplastic elastomer that contains at least a copolymer and a plasticizer. In a molecular weight distribution of a tetrahydrofuran soluble matter of the thermoplastic elastomer measured by gel permeation chromatography, at least one peak is present in each of a region of a molecular weight of 4,000 or less and a region of a molecular weight of 30,000 to 200,000, and a percentage of a component of a molecular weight of 800 or less in a region of a molecular weight of 5,000 or less is 30% or less.