A study of 150 analyses of iron-lithium micas from South China and the other regions indicates that iron-lithium micas are not true binary system minerals but trioctahedral Li-Fe-Al micas, and suggests that iron-lithium micas should be confined as biotite-lepidolite series. Furthermore, the natural subdivision of iron-lithium micas is also made on the basis of the anomalous changes of compositions, refractive indexes and cell parameters.The end-members of iron-lithium micas include K2Li4Al2[Si8O20](OH, F)4, K2Fes [Si6A12O20](OH, F)4, K2Al,[Si6Al2O20](OH, F)4, and K2Fe4Al2[Si4Al4O20](OH, F)4. Three basis vectors, polylithionite substitution(Rvi+2-3Li2 Rvi+3(R1v+3)-1Si, Al-Li musco-vite substitution(Rvi+2)-1Li3(□v1)-1 and muscovite substitution(Rvi+2)-3(Rvi+3)2□v1, are uggested to interpretate the essential changes of iron-lithium mica compositions swhose basic trend is nonlinear and coincident with the orientation of the polylithionite substitution vector--the basic substitution.The members of natural iron-lithum micas includeferrobiotite lithian biotite+ + -- protolithionite--siderophyllite lithian siderophylltte generalized ferrobiotite and siderophyllite zinnwaldite--cryophyllue--lepidolite.Generalized ferrobiotite and siderophyllite are separated by value MF = 4.80(MF = 6(Fe+2 + Mn)/(Fe+2 + Mn + Mg)), but there are no essential difference between them when they are both the members of iron-lithium micas. In fact, the members richer in lithium can be derived from both siderophyllites and ferrobiobites.The value FL = 100Li/(1.5Li + R*)(R* = Fe+3 + Mg + Fev1+3 + Tiv)is more reasonable than the value ol Li-content for describing the basic trend. Abnormal changes of chemical composition at near FL = 5.8, 12.5, 33.3, 49.1 and abnormal changes of refractive indexes Nm and Ng and cell parameters b at FL = 57.1 are the grounds for so-called natural subdivision of iron-lithium micas. The natura subdivision is useful for study of the relations between the iron-lithium micas and the petrogenetic sequence of granites.