Abstract: The radionuclide ²⁴¹Pu decays predominantly by β emission with a half-life 14.29 a. The branching ratio of its α-emission is negligibly small. However, it is difficult to measure the radioactivity of ²⁴¹Pu in a Pu containing complicated sample because of its low β energy. A method for determination of ²⁴¹Pu in high level liquid waste (HLLW) was developed. It consists of the following steps. The first step is to separate and purify plutonium from HLLW. The chemical yield of plutonium is higher than 95%. Secondly, a determination method by using modern liquid scintillation spectrometry combined with isotope dilution, solvent extraction, and ion exchange chromatography was established to analyze the ²⁴¹Pu content in HLLW.