We report on a Chinese family with three members who have CAG repeat expansion in the ataxin-3, two members present with expanded trinucleotide repeat in both the ataxin-3 and tata-binding protein (TBP) and an individual who carries expanded CAG/CAA repeat in the TBP. Only the patients who carry an allele with expansion in the ataxin-3 gene presented with clinical symptoms. This interesting family presents a unique mutation state. We will continue to track this family in the future, which may help us further elucidate the pathogenic mechanism of spinocerebellar ataxia (SCA) type 3 and 17. The study also provides us a novel conception that mutations from two pathogenetic genes may coexist in one patient and SCA-affected patients with intermediate allele need to be further excluded for other SCA subtypes.