The present invention relates to polymorphic forms of (S)-tetrahydrofuran-3-yl 3-(3-(3-methoxy-4-(oxazol-5-yl)phenyl)ureido)benzylcarbamate (Compound 1): ##STR00001## and pharmaceutical compositions thereof. The present invention also relates to processes to prepare compound 1 and pharmaceutical compositions thereof. Compound 1 is an IMPDH inhibitor useful in treating IMPDH-mediated diseases such as immune system related diseases, viral diseases, and cancers.