A brief review is presented on the aspects and mechanism of the metal nonmetal transition in the disordered systems. The electronic and thermo dynamic properties are discussed for expanded Hg and dilute amalgams near the liquid-gas critical point. In expanded liquid Hg a metal-nonmetal (M-NM) transition occurs at density near 9g/cm' and anomalous behaviors are found in the thermodynamic properties such as equation-of-state and isothermal compressibility. At low densities substantial volume contraction and large increase in conductivity are brought about by the addition of a small amount of the elements with high valency such as Bi and Pb to expanded liquid Hg. The semiconductor-metal transition is discussed for liquid and amorphous Se-Te mixtures. In the liquid mixture, the transition from Se-like loosely packed to Te-like densely packed structure occurs by changing the temperature, pressure and Te content. The transition may be associated with the change in the short-range order around Te atoms. In amorphous Seo.aTeo.s mixture a reproducible sharp semiconductor-metal transition is found under pressure. The semiconductor-metal transition near the liquid-liquid critical point is also described for liquid Tl-Se mixtures in the Se-rich region. The liquid-liquid two-phase region is diminished by the application of pressure. It is suggested that the metal-nonmetal transitions observed in the liquid and amorphous systems are closely related to the structural changes.