GM1 gangliosidosis is a glycosphingolipid (GSL) lysosomal storage disease caused by a genetic deficiency of acid b-galactosidase (b-gal), the enzyme that catabolyzes GM1 within lysosomes. Accumulation of GM1 and its asialo form (GA1) occurs primarily in the brain, leading to progressive neurodegeneration and brain dysfunction. Substrate reduction therapy aims to decrease the rate of GSL biosynthesis to counterbalance the impaired rate of catabolism. The imino sugar N-butyldeoxygalactonojirimycin (N B-DGJ) is a competitive inhibitor of the ceramide-specific glucosyltransferase that catalyzes the first step in GSL biosynthesis. Neonatal C57BL/6J (B6) and b-gal knockout (-/-) mice were injected daily from post-natal day 2 (p-2) to p-5 with either vehicle or N B-DGJ at 600 mg or 1200 mg/kg body weight. These drug concentrations significantly reduced total brain ganglioside and GM1 content in the B6 and the b-gal (-/-) mice. Drug treatment had no significant effect on viability, body weight, brain weight, or brain water content in the B6 and b-gal (-/-) mice. Significant elevations in neutral lipids (GA1, ceramide, and sphingomyelin) were observed in the N B-DGJ-treated b-gal (-/-) mice, but were not associated with adverse effects. Also, N B-DGJ treatment of B6 and b-gal (-/-) mice from p-2 to p-5 had no subsequent effect on brain ganglioside content at p-21. Our results show that N B-DGJ is effective in reducing total brain ganglioside and GM1 content at early neonatal ages. These findings suggest that substrate reduction therapy using N B-DGJ may be an effective early intervention for GM1 gangliosidosis and possibly other GSL lysosomal storage diseases.