α‐Hydroxy and α‐chloroformyl oligomers of poly(butylene terephthalate) (PBT) were prepared in 1,1,2,2‐tetrachloroethane by condensing terephthaloyl chloride and 1,4‐butanediol and using benzoyl chloride and 4‐hydroxybutyl benzoate as chain limitator. The average molecular weight was determined by 1H NMR analysis, and thermal properties were assessed by differential scanning calorimetry (DSC). Preparation of α‐thiol oligomers of PBT was also investigated by esterification of α‐hydroxy oligomers with thioglycolic acid and using p‐toluenesulfonic acid as catalyst. The DSC and TGA analyses pointed out that the introduction of a thiol group by esterification has no influence on the thermal properties of the PBT oligomers.