Abstract: This invention relates to new methods of treating parasitic infections, such as trichomonas vaginalis infection and cecum amoeba infection, using L-enantiomer enriched ornidazole, in particular enantiomerically pure L-ornidazole, which provides benefits such as higher efficacy and lower toxicity to central nervous system over the existing racemic Ornidazole drug. New methods of synthesizing L- and D-enantiomers of Ornidazole in high purity and enantiomeric excess (ee), new formulations of the enantiomerically enriched L- or D-ornidazole, as well as their preparation processes and methods of use, are also disclosed.