Abstract: The theoretical and numerical studies on kinetic micro-instabilities, including ion temperature gradient (ITG) driven modes, trapped electron modes (TEMs) in the presence of impurity ions as well as impurity modes (IMs), induced by impurity density gradient alone, in toroidal magnetized plasmas, such as tokamak and reversed-field pinch (RFP) are reviewed briefly. The basic theory for IMs, the electrostatic instabilities in tokamak and RFP plasmas are discussed. The observations of hybrid and coexistence of the instabilities are categorized systematically. The effects of impurity ions on electromagnetic instabilities such as ITG modes, the kinetic ballooning modes (KBMs) and kinetic shear Alfvén modes induced by impurity ions in tokamak plasmas of finite β (=plasma pressure/magnetic pressure) are analyzed. The interesting topics for future investigation are suggested.