We reported a 74-year-old male case of progressive supranuclear palsy (PSP) who responded to tandospirone citrate, a serotonin receptor (5-HT1A) agonist. The patient manifested postural instability and gait disturbance at 71 years. Additionally, he showed vertical gaze paresis, regidity of the neck, extremities and trunk, bradykinesia and mild cognitive impairment. A brain MRI revealed moderate atrophy of bilateral frontal/temporal lobes and of midbrain tegmentum one year after the onset. The patient had been diagnosed as PSP and treated with L-DOPA. However, L-DOPA therapy showed only transient response for a few months. His symptoms deteriorated gradually, and he became unable to sit, stand up or walk by himself. Tandospirone citrate was additionally administered at 30 mg/day. Rigidity and bradykinesia were remarkably improved in two weeks after the start of tandospirone treatment. He became able to stand up and walk a short distance with supports in four weeks. Cognitive disturbance was also slightly improved. Tandospirone citrate was effective on our case of PSP, especially on rigidity. Our findings suggest that combination of levodopa and tandospirone citrate is a useful therapy for PSP.