Abstract: This invention is concerned with the automatization of the efficiency tracing method in liquid scintillation measurement. In a conventional efficiency tracing method, the radioactivity has been determined by changing in turn several kinds of measurement conditions and by manually drawing a graph. In order to overcome these inconveniences, the present invention provides a measuring method and apparatus therefore in which the measurement region of a pulse height analyzer which is determined by a lower level and an upper level is fixed in a liquid scintillation counter, a data group obtained by measuring the counting efficiency of a standard sample and the counting rate of a subject sample is automatically determined from the regression equation. Thus the efficiency tracing method has become extremely convenient and its utility has been significantly improved.