Abstract: The half life of the long lived fission product 126 Sn has been measured by Inductively Coupled Plasma Mass Spectrometry(ICP MS). The dietheyl ether is used as an extractant to separate carrier free 126 Sn from high level radioactive liquid waste diluted in 0.1 mol/L HCl 1.0 mol/L NH 4SCN medium. The 126 Sn sample is divided into two portions, one for measuring the 126 Sn activity by HPGe γ spectrometer, and the other for measuring the number of 126 Sn nuclei by ICP MS. The portion for activity measurement has been further purified through a radiochemical procedure with Sn carrier before γ spectrum is measured. The obtained value of the half life of 126 Sn is (2.48±0.26)×10 5 a.