Stability of fassaitic pyroxene in the system CaMgSi2O6-CaFeAlSiO6-CaAl2SiO6-CaTiAl2O6 is discussed on the basis of published data. In the system CaMgSi2O6-CaFeAlSiO6 the stability field of clinopyroxene decreases with an increase in CaFeAlSiO6 content and a decrease in oxygen fugacity at constant temperature. The stability field of clinopyroxene in the system CaMgSi2O6-CaAlFeSiO6-CaAl2SiO6 is strongly influenced by oxygen fugacity at low and high pressure and decreases with respect to CaFeAlSiO6 component. Titanium content of the clinopyroxene does not seem to be affected by the change of oxygen fugacity when magnetite is stable. These data are probably useful in evaluating the condition under which natural fassaitic pyroxenes are formed.