PSP is a relentlessly progressive neurodegenerative disorder, clinically characterized by parkinsonism with prominent axial involvement and postural instability, bulbar symptoms, supranuclear ophthalmoplegia, and executive dysfunction. Abnormal neuronal and glial tau aggregations affecting the basal ganglia and selective brainstem structures result in dysfunction of the five frontosubcortical circuits and brainstem functions. There is no effective treatment for PSP. One of the key feature in the aggregation of tau is its phosphorylation by kinases such as glycogen synthase kinase 3b (GSK3b). Recent reports have shown that valproic acid was able to inhibit the activity of GSK3b and could exert a neuroprotective effect through this inhibition. We thus decided to conduct this controlled study to assess the putative neuroprotective effects in patients with PSP.