In this study, we examined the biofilm forming ability, the mRNA expression of curli genes and the morphologies of curli fimbriae and biofilms in clinical isolates of Enterobacter cloacae. The csgBA operon was found in 11 (78.6%) of the 14 isolates. The ability of E. cloacae isolates to form biofilms was significantly correlated with the mRNA expression level of the csgA and csgD genes. The curli protein fimbriae appeared as tangled fibers and the curli-proficient strain formed mature biofilms. Our data suggest that the expression of the curli fimbriae play an important role in biofilm formation in E. cloacae.