Hydrogen sulfide (H₂S) is known as a toxic gas, but has been focused as a biological mediator, which modulates signal transduction and protects cells and tissues from oxidative stress. Endogenous H₂S is mainly generated from L-cysteine, while a novel biogenesis pathway of H₂S from D-cysteine has been recently identified. In this pathway, D-amino acid oxidase (DAO) converts D-cysteine to 3-mercaptopyruvate (3MP), followed by the generation of H₂S from 3MP by 3-mercaptopyrvate sulfurtransferase. DAO is especially abundant in cerebellum among various brain regions and mediates efficient generation of H₂S from D-cysteine in the cerebellar tissues. Cerebella Purkinje cells (PCs) are characterized by the highly-branched dendrites and are important for cerebellar functions. The dendritic shrinkage and degeneration of PCs are frequently observed in patients and model mice of cerebellar ataxias. We revealed that D-cysteine enhances dendritic development of primary cultured PCs, but L-cysteine does not. This effect was inhibited by DAO inhibitors and reproduced by 3MP and a H₂S donor, suggesting that this enhancement by D-cysteine is caused by the production of H₂S. Taken together, D-cysteine would be available as a neuroprotectant against cerebellar ataxias.