Abstract: The surface charge is one of the most important properties of liposomes. In this paper surface potential of liposomes was measured by fluorimetry using 1,8-ANS as a probe and by microelectrophoresis. The encapsulation efficiency and leakage rate of ionic drugs were influenced by the surface charge of liposomes. Higher encapsulation efficiency and lower leakage rate were resulted, if the surface charge of liposomes was opposite to the ionic charge of encapsulated drug.Mice infected with toxoplasma were used as a model. In in vivo test, liposomedrug was compared with the free drug. The. average survival days of groups of liposome-drugs were much longer than that of the group of free drugs.Mouse infected with toxoplasma is a simple, convenient and accurate model for measuring the biological activation of liposome-drugs.