[en] The procedure of analysis of tritium, which emits low energy beta ray, is described. It is important to measure the environmental concentration of tritium, therefore in this report, the method of analysis for environmental samples is described. Samples of measurement are collected from inland water, drinking water, sea water, precipitation, air (water vapour), and biological samples. The collected samples are distilled before the measurement to remove the impurities. The distilled samples are changed to the samples for the measurement with a liquid scintillation counter. The liquid scintillator to be added to the samples is made from some fluorescent substance by dissolving it into solvent. The standard quenching substance is also prepared. The quantitative measurement of tritium is made with a scintillation counter according to the manual of the counter for the optimum measurement. Correction and analysis of the obtained data are made by following the procedure described in this manual. In the reference material of this manual, the principle of the present method and the instruments are explained. The method of electrolytic concentration is also presented in the reference material. (Kato, T.)