A novel bacterium was isolated and characterized from the amniotic fluid of a woman who experienced intrauterine fetal demise in the second trimester of pregnancy. The bacterium was a slow-growing, gram-negative anaerobic coccobacillus belonging to the genus Leptotrichia. Unlike Leptotrichia sanguinegens, the isolate did not grow in chopped-meat glucose broth or on sheep blood agar upon subculturing. The isolate was characterized by sequencing and analyzing its 16S rRNA gene. The 1,493-bp 16S ribosomal DNA sequence had only 96% homology with L. sanguinegens. Several phylogenetic analyses indicated that L. amnionii is a distinct species and most closely related to L. sanguiegens.