To tract the intracellular localization of the hypothetical protein CT058 in the Chlamydia trachomatis-infected cells. The gene ct058 was expressed as GST-CT058 fusion protein in E. coli and its antibody was prepared by immunizing mouse with the fusion protein. Then, the anti-GST-CT058 an-tibody was used to localize the endogenous protein in cells infected by C. trachomatis serovar L2 using indirect immunofluorescence assay (IFA). Western blot was carried out to detect whether CT058 pre-sents in the purified elementary body (EB) or reticulate body (RB). The anti-GST-CT058 antibody de-tected an inclusion-inside signal in an IFA. The intra-inclusion signal could be removed by pre-absorption of the antibody with the GST-CT058 fusion protein but not control GST-CT232. Fur-thermore, the mouse anti-CT058 antibody recognized the endogenous CT058 protein from purified EBs and RBs in a Western blot assay. The results of the current study support the general consensus that the hypothetical protein CT058 was localized within the inclusion body of the C. trachomatis-infected cells.