This study is a molecular and genetic study focused on the importance of the enzyme Serine Palmitoyltransferase and its role in the life cycle of the parasite Leishmania mexicana in the two forms of the parasite, amastigotes and promastigotes. Cytotoxicity test established for amastigotes and promastigotes by adding the “myriocin” which inhibits the sphingolipids biosynthesis to explore the ability of the parasite to survive proliferate and infect the host’s cells (macrophages). To examine the ability of the parasite for infection after myriocin treatment, an ex vivo infection has designed with the macrophage cell line of mouse (RAW264.7) and the result was positive in which the parasite succeeded to infect the macrophages. To explain this result, it was discovered, for the first time of this species (L. mexicana) that it has the ability of de novo sphingolipid biosynthesis without the salvage of the sphingolipid of the host (macrophage) and it was found that this parasite can synthesize the protein SPT by the two forms of the parasite (amastigotes and promastigotes). These results were corroborated by the evaluation of the gene expression of the SPT2 of the macrophages in which the result of kinetic expression (quantitative real time PCR) found that there was no significance between the gene expression of SPT in test and control groups (infected and non-infected macrophages) which confirms that the parasite did not salvage the macrophage sphingolipid but it synthesized its own sphingolipid. This study was conducted at the department of Bio-medical sciences, Durham University, UK.