Abstract: Although berberine had been used as an antibacterial, yet its physical and chemical properties responsible for the biological effects were not fully investigated. In this re- port, the Pka values of berberium chloride were determined spectrometrically both in water and in ethanol and were found to be 15.23 and 13.05 respectively. The Pka value in water is very different to that obtained by Kolthoff. Discussion is made from the view point of molecular structural theory and experimental data. Some suggestions concerning the relation between its basicity and biological effects, such as absorption, excretion etc, were presented.