A comparison between the molecular structure of conventional and low molecular weight hydroxyl terminated polybutadienes (HTPBs) is presented. The conventional HTPB samples were R45M, R45HT (Atochem), Liquiflex P and H (Petroflex, Brazil), and the low molecular weight ones were R20LM (Atochem) and two laboratory synthesized materials. The structural differences found were attributed to dissimilarities in fabrication processes for each type of HTPB. Some mechanistic pathways for the polymerization are suggested.