This paper reviews how some of the structural variables influence the mesomorphic properties of main chain polyesters. Among the many possible variables 1) linking order of the ester group, 2) comonomer sequence, 3) regioregularity of substituents, and 4) location of the substituents are the four important structural factors to be discussed about. A close examination of the dependence of the thermal and liquid crystalline properties of the main chain thermotropic polyesters on their microchemical structures provides us with an insight how to control their macroscopic properties.