[en] Some methods for the analysis of I-129 in the environment are described. Iodide ion in seawater is coprecipitated with chloride ion by silver citrate powder, and that in seaweeds and in sediment is sublimated by heating at about 900⁰C in O₂ atmosphere, and then the iodine is trapped in cooled NaOH and NaHSO₃ mixed solution. The trapped iodine is precipitated with AgNO₃ solution for γ-/X-ray spectrometry (detection limit asymptotically equals 30 pCi), or extracted into toluene scintillater solution for liquid scintillation counting. The decomposition of AgI is necessary for low level I-129 measurement; The AgI was transfered in a flask, added with 2N H₂SO₄ and Zn sand, and decomposed by stirring for 2 hr. Filtered the solution, added 0.5 g of NaNO₂ and toluene scintillater to extract the iodine then added 1 ml of 2-methyl 1-butene to decolorize, the solution is measured by a liquid scintillation counter (detection limit asymptotically equals 1 pCi). This method can be applied for monitoring of low level radioactive water waste. (auth.)