Cystathionine β-synthase () deficiency is a recessive inborn error of metabolism characterized by extremely elevated total homocysteine (tHcy) in the blood. Patients diagnosed with CBS deficiency have a variety of clinical problems， including dislocated lenses， osteoporosis， cognitive and behavioral issues， and a significantly increased risk of thrombosis. Current treatment strategies involve a combination of vitamin supplementation and restriction of foods containing the homocysteine precursor methionine. Here， a mouse model for CBS deficiency () was used to evaluate the potential of minicircle-based naked DNA gene therapy to treat CBS deficiency. A 2.3?kb DNA-minicircle containing the liver-specific P3 promoter driving the human cDNA (MC.P3-hCBS) was delivered into mice via a single hydrodynamic tail vein injection. Mean serum tHcy decreased from 351?μM before injection to 176?μM 7 days after injection (?=?0.0005)， and remained decreased for at least 42 days. Western blot analysis reveals significant minicircle-directed CBS expression in the liver tissue. Liver CBS activity increased 34-fold (12.8 vs. 432 units; ?=?0.0004) in MC.P3-hCBS-injected animals. Injection of MC.P3-hCBS in young mice， subsequently followed for 202 days， showed that the vector can ameliorate the mouse homocystinuria alopecia phenotype. The present findings show that minicircle-based gene therapy can lower tHcy in a mouse model of CBS deficiency.