A polybutylene naphthalate polyester and process for preparing polybutylene naphthalate polyester, for improving barrier performance of polyesters used in making of monolayer or multilayer containers. The process comprising: a) mixing butane diol with polymerization catalysts, monoethylene glycol, color toner, and at least one crystallization suppressing agent; b) reacting said mixture with naphthalene dicarboxylic acid or ester thereof to obtain oligomerized product via esterification or ester interchange; c) polymerizing said oligomer using at least one polymerization catalyst to obtain amorphous polybutylene naphthalate polyester chips; d) crystallizing said polybutylene naphthalate polyester chips; and e) subjecting said polyester chips to solid state polymerization to upgrade the intrinsic viscosity (I.V.) up to more than 0.40 dl/gm.