[en] The mass of supernovae which synthesize r-process elements has been estimated to be between 2 m/sub sun/ and 10m/sub sun/. This estimation is based on the reqiurement of the nucleocosmochronology models that the heavy-element enrichment rate of the gas in the Galaxy have been approximately constant throughout its life. The star-formation rate derived by M. Schmidt has been used for calculations. The calculated range is in good agreement with other estimates. It is suggested that supermassive stars either are formed rarely or do not expel r-process elements