In the present study, the concentration-dependent activity and activity coefficients of K and Li in liquid bismuth at 973 K and 1023 K were determined by electromotive force measurement (emf) which was performed in an electrochemical cell: K (Li)-Bi (reference) parallel to molten salt electrolyte parallel to liquid Bi (working). Instead of simply mixing Bi and K or Li for different compositions of working electrode, various compositions of the working electrode were acquired by coulometric titrating different quantities of K and Li into liquid bismuth through chronopotentiometry electrolysis. The present method of tracking the change of activity and activity coefficient can be continuously operated for multiple measurements with different Bi-K/Li compositions, therefore, the measurements can provide a more accurate relationship between activity coefficient and the concentration of K (Li) in liquid Bi. (c) 2019 The Electrochemical Society.