The characteristic temperatures of the selected quaternary CaO-MgO-Al2O3-SiO2 slags have been measured by the hemisphere method. The effects of the basicity value and Al2O3 content studied. The results indicated that basicity and the Al2O3 content had obvious influence on the characteristic temperatures of the selected slags. All of the softening temperature, the hemisphere temperature and the flow temperature decrease with the increasing of the basicity value. Under the same content of CaO, the characteristic temperature decreased sharply by adding Al2O3. The solidus and liquidus temperatures computed from the FactSage database were compared with the present experimental observations as well as the melting temperature information of the DSC measurements. The results also indicated that it is possible to get a reasonable idea of the solidus temperature from the hemisphere temperature while the flow temperature would indicate the liquidus temperature.