Niemann–Pick disease type C1 (NPC1) is a fatal congenital neurodegenerative disorder caused by mutations in the NPC1 gene, which is involved in cholesterol transport in lysosomes. Broad clinical manifestations of NPC1 include liver failure, pulmonary disorder, neurological deficits, and psychiatric symptoms. The main cause of death in NPC1 patients involves central nervous system (CNS) dysfunction; there is no essential treatment. We generated a tyrosine-mutant adeno-associated virus (AAV) 9/3 vector that expresses human NPC1 under a cytomegalovirus (CMV) promoter (AAV-CMV- hNPC1 ) and injected it into the left lateral ventricle (5 μL) and cisterna magna (10 μL) of Npc1 homo-knockout ( Npc1 − / − ) mice. Each mouse received total 1.35 × 10 11 vector genome on days 4 or 5 of life. AAV-treated Npc1 − / − mice ( n = 11) had an average survival of >28 weeks, while all saline-treated Npc1 − / − mice ( n = 11) and untreated Npc1 − / − mice ( n = 6) died within 16 weeks. Saline-treated and untreated Npc1 − / − mice lost body weight from 7 weeks until death. However, the average body weight of AAV-treated Npc1 − / − mice increased until 15 weeks. AAV-treated Npc1 − / − mice also showed a significant improvement in the rotarod test performance. A pathological analysis at 11 weeks showed that cerebellar Purkinje cells were preserved in AAV-treated Npc1 − / − mice. In contrast, untreated Npc1 − / − mice showed an almost total loss of cerebellar Purkinje cells. Combined injection into both the lateral ventricle and cisterna magna achieved broader delivery of the vector to the CNS, leading to better outcomes than noted in previous reports, with injection into the lateral ventricles or veins alone. In AAV-treated Npc1 − / − mice, vector genome DNA was detected widely in the CNS and liver. Human NPC1 RNA was detected in the brain, liver, lung, and heart. Accumulated unesterified cholesterol in the liver was reduced in the AAV-treated Npc1 − / − mice. Our results suggest the feasibility of gene therapy for patients with NPC1.