This article describes the analysis of polybutadiene terephthalate (PBT) resin. PBT resins are widely used in various applications due to their excellent toughness and resistance to damage. The molecular weight distribution is a key measure for assessing resin degradation and estimating the mechanical strength of the final product. The analysis of PBT was performed using gel permeation chromatography (GPC) in the polar organic solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). The article discusses the use of Agilent PL HFIPgel columns for the analysis at 40°C, with detection using differential refractive index and viscometry. GPC coupled with a molecular weight sensitive viscometer allows for the calculation of molecular weights based on hydrodynamic properties.