Main -chain dimer liquid crystal having structure such as NCO(CH2)nOCN(CBA-9,10_and BrO(CH2)nOBr(BrBA-9,10) with n=9,10 were synthesized. CBA-9 and 10 are known to form nematic mesophases. While BrBA-9 does not show any mesophase by microscopic examination, BrBA-10 exhibits mesophases on cooling; transition to a simple fan-shaped texture (A) followed by a mosaic texture (E). For a comparison purpose, a hybrid compound NCO(CH2)100Br(CBrBA-10) was also prepared. Phase diagrams were constuctured for binary mixtures comprising BrBA-9/CBA-9, BrBA-10/CBA-10 and CBA-10/CBrBA-10. The eutectic temperature and eutectic composition were calculated from the DSC data using the Schoder-van Laar equation. The results were found to be consistent with those observed. For the CBA-10/BrBA-10 system the orientational order parameter of CBA-10 was determined in the nematic state by the H-NMR method. The order parameters of the mesogenic core remain almost identical with those of the pure compound when compared at given reduced temperature T/Tn