Formation of intracellular aggregates is the hallmark of polyglutamine (polyQ) diseases. We analyzed the components of purified nuclear polyQ aggregates by mass spectrometry. As a result, we found that the RNA-binding protein translocated in liposarcoma (TLS) was one of the major components of nuclear polyQ aggregate-interacting proteins in a Huntington disease cell model and was also associated with neuronal intranuclear inclusions of polyQ diseases. In vitro study revealed that TLS could directly bind to truncated N-terminal huntingtin (tNhtt) aggregates but could not bind to monomer, indicating that the tNhtt protein acquired the ability to sequester TLS after forming aggregates. Immunohistochemistry showed that TLS was associated with neuronal intranuclear inclusions of Huntington disease and other poly Q disease brains. After this report, FUS/TLS was reported as a responsible gene for ALS6. Because TLS has a variety of functional roles, the sequestration of TLS to polyQ aggregates may play a role in diverse pathological changes in the brains of patients with polyQ diseases and ALS6.