Abstract : Typhoid fever is a infectious disease caused by Salmonella typhi (S.typhi), and is one of the leading causes of mortality and morbidity of deaths worldwide. New antibacterial sources can be obtained from bioactive compounds contained in a plant, one of which is from the seagrass Thalassia hemprichii contains bioactive compounds that have the potential to be antibacterial, antifungal, anti-protozoa, antiviral, antifertility, and medicinal substances that affect the cardiovascular system, and have bioactive potential as antioxidants, and also contain phenolic compounds. This study aims to prove that the Thalassia hemprichii extract influences the Toll-Like Receptor 4 (TLR4) mRNA expression in the BALB/c mice when administered with the Thalassia hemprichii extract, before and after injected with S. typhi. The mRNA extraction uses the guanidium thiocyanate (GuSCn) and the examination of TLR4 mRNA expression by the Realtime PCR. The results of this study revealed that there was an influence of the Thalassia hemprichii extract on TLR4 mRNA expression on the BALB/c mice both in before and after injected with S. typhi