This is a part of our systematic research work on polyimides with mesogenic unit side chain. In this study, a new 4′-phenylphenyl 4-(3″,5″-diaminobenzoyloxy)benzoate and polyimide were synthesized, and characterized by FTIR, 1H-NMR, inherent viscosity, mechanical properties,and solubility measurements. The diamine composed with mesogenic unit aryl ester groups and biphenyl group with longer L/D ratio, was synthesized by two key steps. Firstly, the hydroxy group of 4-hydroxybenzoic acid was protected by acetoxy group for avoiding self- polymerization of 4-hydroxybenzoic acid, and then selectively hydrolyzed after esterification of carboxyl.Secondly, a selective catalysis hydrogenation was adopted to prevent the aryl ester from deoxidation. Based on this diamine, a novel polyimide was prepared by polycondensation of 4′-phenylphenyl 4-(3″, 5″-diaminobenzoyloxy)benzoate and 4-aminophenyl ether(ODA) with 4,4′-oxydiphthalic anhydride(ODPA) in N-methyl-2-pyrrolidone (NMP). The resulting polyimide with longer side chain showed better solubility and more regular structure. Its inherent viscosity is lower than that without side chains, but its modulus and strength not only maintained, even improved.