The direct polycondensation of dicarboxylic acids with diols using diphenylammonium triflate (DPAT) as catalyst is described. We investigated the solvent effect on molecular weight in the polyesterification reactions, influence of the reaction period for a fixed catalyst amount. Also, to determine the effect of catalyst the reaction between succinic acid and 1,6-hexanediol using different catalyst amounts for the constant time was examined. Different types of polyesters were synthesized via solution polycondensation using DPAT catalyst. Molecular weights of the synthesized polymers were determined using GPC and an Ubbelohde viscosimeter. It is found that the molecular weights of polyhexamethylene succinate, polyhexamethylene adipate, polydecamethylene adipate, polyhexamethylene sebecate, polybutylene adipate and polyethylene adipate, are 12900 g/mol, 13300 g/mol, 8400 g/mol, 8100 g/mol, 2750 g/mol and 2600 g/mol, respectively. The polyesters were characterized by H-1 NMR and FTIR spectroscopy. DPAT gave the highest yields of polyhexamethylene succinate and polydecamethylene adipate (93%). It is found that toluene is the best solvent, an appropriate reaction period is 12 h and the optimum catalyst amount is 0.25 mol% for polyesterification. DPAT is efficient for the synthesis of aliphatic polyesters under mild conditions because of the polycondensation, it was revealed that DPAT seems to catalyze not only the esterification but also etherification is catalyzed as a side reaction.