This paper studies how the electrolyte conductivity has effects on the performance of an alkaline water electrolyzer. A mathematical model of the electrolyte conductivity between two electrodes has been developed based on a combination of electrolyte conductivity, void fraction and velocity of bubble rising in a liquid. The Design of Experiment technique along with statistical method is used to develop the empirical model to investigate the correlation between void fraction, current and solution temperature. The mathematical results show that the drop of the electrical conductivity is caused by an increase of solution temperature and the height of electrode. On the other hand, an increase of bubble diameter results in an increase of conductivity. Subsequently, the mathematical results are compared with the experimental results where the void fraction obtained from the model agrees well with those obtained from the experimental results.