Type B Niemann-Pick disease is an autosomal recessive sphingolipidosis due to mutations in the sphingomyelin phosphodiesterase 1 gene (SMPD1).Here we present molecular findings for two sibling patients.One mutation V36A due to c.107T＞C in exon 1 is a single nucleotide polymorphism and the other N522S due to c.1565 A＞G in exon 6 is a novel missense mutation.This non-fatal missense mutation leads to -20％ residual lysosomal acid sphingomyelinase activity in vitro and only results in hepatosplenomegaly without neurologic involvement.