The invention relates to a process for producing 228Th from a natural thorium salt, which comprises in succession: a) the separation of the radium from the other radioelements present in this salt, by at least one coprecipitation of the radium by barium sulphate, this coprecipitation comprising: i) the addition of sulphuric acid and a barium salt to an aqueous solution of said natural thorium salt in order to form a barium-radium sulphate coprecipitate and ii) the separation of the coprecipitate from the medium in which it has formed； b) the extraction of the thorium 228 coming from the decay of radium 228 from the coprecipitate thus separated； and, optionally c) the purification and concentration of the 228Th thus extracted. Applications: manufacture of radiopharmaceutical products useful in nuclear medicine, in particular in radioimmunotherapy for the treatment of cancers and AIDS.
