Chlamydia trachomatis is an obligate intracellular bacterial pathogen responsible for sexually transmitted infections. A number of C. trachomatis chaperones and proteases such as the periplasmic high-temperature requirement protein A (HtrA) have been previously demonstrated to be important for bacterial protein folding and stress response [1]. However, the function of HtrA in chlamydial infection and virulence is not well elucidated. Therefore, this project aims to determine the potential role of CtHtrA in chlamydial infection and pathogenesis by using the chemical inhibitor compound of HtrA activity, compound 1. The effect of the HtrA inhibitor on the growth and viability of C. trachomatis as well as on the viability of C. trachomatis - infected host cells in the absence or presence of the compound was assessed. The morphology and presence of chlamydial HtrA and MOMP as well as specific host proteins SQSTM1 and LAMP1 in the presence of compound 1 or DMSO (control) treatments was also determined through confocal immunocytochemistry. It was observed that 100 µM compound 1 was toxic to C. trachomatis for all time points post-infection. Determination of the viability of C. trachomatis-infected host cells in the presence of HtrA inhibitor indicates that compound 1 is not toxic to host cells. Confocal immunocytochemistry revealed that there was a significant difference on the size of the inclusion formed between compound 1- and DMSO- treated infected cells, indicating the chlamydial inclusions fail to develop after HtrA inhibition. No co-localization was observed between the inclusions and lysosomal markers as well as between chlamydial inclusions and sequestosome, indicating that the failure of the inclusions to develop does not relate to the two most common host defence pathways. Therefore, HtrA inhibition leads to a failure of chlamydial inclusions to grow in size without killing the host cells and this failure to develop does not appear to involve the host defence lysozome or autophagy pathways.