Binary mixture of 4 octyloxy- 4’-cyanobiphenyl (80CB) and 4-n-hexyl phenyl 4-n’ pentyloxy benzoate (ME 50.6) shows enhanced smectic A phase, where 80CB has both nematic and smecticA phases and ME 50.6 has only nematic phase. In the present paper we report the phase diagram, refractive indices, densities and orientational order parameters of different binary mixtures of 80CB/ME 50.6 throughout the entire composition range. BireFringence as well as density values show minima with mole fraction of 80CB. Order of smectic to nematic phase transition has been discussed.