Novel crystalline forms of anti Pneumocystis carinii compound (2-[4-(4-Chlorophenyl)cyclohexyl]-3-hydroxy-1,4-naphthoquinone) commonly known as Atovaquone and methods for producing the same is disclosed herein. This also provides pharmaceutical compositions comprising the said polymorphs of Atovaquone and method of treating Pneumocystis carinii pneumonia, the method comprising administering to a warm blooded animal an effective amount of a product-by-process composition of matter comprising polymorphic forms of Atovaquone.