[en] A simple method for the determination of the radon emanation fraction (EF) from rocks has been studied in this work. Growth and decay curves of radium-radon-daughters and the double counting technique using the same gamma-ray spectrometry were applied to determine the EF from eleven rocks at different lithologies. Aluminium Marinelli beakers were used to prevent the leakage of radon during the equilibration period of around 30 days. And also, nitrogen purging system was constructed to replace the surrounding air of the detector for obtaining a stable background and reducing the interference of radon daughter nuclides from the atmosphere. (author)