Alpha-Lipoic acid has recently been permitted for use in foodstuffs and is contained in tablets and capsules. Although alpha-lipoic acid is synthesized from adipic acid, the safety of polymers produced during the purification and drying processes has been an issue of concern. Hence, we examined the safety profiles of thermally denatured polymer (LAP-A) and ethanol-denatured polymer (LAP-B) produced in the manufacturing process of alpha-lipoic acid. Furthermore, we conducted structural analysis of these polymers by 1H-NMR and FAB-MS spectroscopy. In a consecutive ingestion test, male and female mice ingested diet containing 0.1 and 0.2% LAP-A and -B for 4 weeks. Blood uric acid, potassium and lactate dehydrogenase (LDH) tended to increase without dose-dependency. Relative liver weights were also increased. However, male dogs that were orally administered LAP-B (500 mg/kg) once did not show any abnormalities in blood parameters or general condition. These findings indicate that alpha-lipoic acid polymers are not acutely toxic; however, chronic ingestion of these polymers may affect liver and kidney functions.