In the present paper we give explicit analytical formulas for the number of Kekule structures of homologous series of hexagonal systems (Ai1Ai2)n and (Bj1 Bj2)n (1≤i1
i2≤4; i≤j1
J2≤0). Our method is based on the theory of linear recursion relations and simultaneous consideration of a group of mutually related homologous series.