The destruction of the intercalated smectic A structure of a laterally bulky branched 1,4-phenylen dibenzoate A by addition of a rodlike cinnamate B was studied by the phase diagram as well as by calorimetric, x-ray and dielectric measurements. The thermal stability of the S(A) phase of compound A and its phase transition enthalpy decrease with increasing concentration of B. Furthermore, the destruction of the short range order of A is characterized by increasing layer distances, decreasing dipolar correlation and an increasing dielectric relaxation frequency only of component A.