The solubility of oxygen in liquid lead bismuth eutectic (LBE) was determined by using electrochemical methods. The oxygen partial pressure in oxygen saturated LBE was measured from 475 to 724 K by using an oxygen sensor comprised of yttria partially stabilized zirconia and air/LSM (Lanthanum strontium manganite) reference electrode. Sieverts’ constant of the dissolved oxygen in LBE was measured from 598 to 748 K by coulometric titration method using the oxygen sensor. The measured oxygen partial pressure in oxygen saturated LBE (PO2(LBE−PbO) in bar) and Sieverts’ constant of dissolved oxygen in LBE (k for 1 wt.% standard state) are given by log PO2(LBE−PbO) = 11.52 − 22996/T (475-724 K), log k = 3.12 − 7072/T (598-748 K) respectively. Combining the measured data, the oxygen solubility in LBE (CO,S in wt.%) was derived and it is given by logCO,S = 2.64 − 4426/T (598-724 K).