The two-component system octyloxycyanobiphenyl (80CB) + decyloxycyanobiphenil (100CB) has been studied by means of modulated differential scanning calorimetry as well as optical microscopy. The general trends of the phase diagram are similar to the two-component system octylcyanobiphenyl (8CB) + decylcyanobiphenil (10CB), previously published. Evidence for the existence of a TCP have been reported. the molar composition being about 0.33 of 100CB. Additionally, the smectic mesophase of the 80CB + 100CB mixtures has been unmistakably characterized through optical measurements as smectic A for the whole composition range.