Spinocerebellar ataxia type 32 (SCAR32) is a rare autosomal neurodegenerative disorder caused by mutations in the peroxiredoxin 3 (PRDX3) gene, which encodes a mitochondria-specific antioxidant enzyme critical for maintaining cellular redox homeostasis. Here, we reported a case of a homozygous nonsense mutation (c.619 C > T; p.Arg207*) in PRDX3 of a 12-year-old Chinese boy. This mutation was predicted to result in premature termination of protein translation. Consequently, the patient presented with slowly progressive gait ataxia and cerebellar vermis atrophy. Mild cognitive impairment was also observed, with deficits in perceptual reasoning and processing speed. Additionally, he showed increased thyroid autoantibodies and thyroid enlargement. This case broadens the phenotypic spectrum of PRDX3-related disease, highlights its genetic and clinical heterogeneity, and reinforces the importance of early genetic testing in paediatric ataxia.