###### Abstract  
_Cymbopogon winterianus_, known as \"citronella grass\", is an important aromatic and medicinal tropical herbaceous plant. The essential oil of _C. winterianus_ (EOCw) is popularly used to play an important role in improving human health due to its potential as a bioactive component. The present study aimed to identify the components of the essential oil of _C. winterianus_ and verify its leishmaniasismaticidal and trypanicidal potential, as well as the cytotoxicity in mammalian cells, in vitro. The EOCw had geraiol (42.13%), citronellal (17.31%), and citronellol (16.91%) as major constituents. The essential oil only exhibited significant cytotoxicity in mammalian fibroblasts at concentrations greater than 250 \(\mathrm{\SIUnitSymbolMicro mall}\), while regarding antipromastigote and antiepimastigote activities, they presented values considered clinically relevant, since both had LC50 \(<\) 62.5 \(\mathrm{\SIUnitSymbolMicro mall}\). It can be concluded that this is a pioneer study on the potential of the essential oil of _C. winterianus_ and its use against the parasites _T. cruzi_ and _L. brasiliensis_, and its importance is also based on this fact. Additionally, according to the results, _C. winterianus_ was effective in presenting values of clinical relevance and low toxicity and, therefore, an indicator of popular use. C. winterianus; geraiol; cytotoxicity; leishmaniasismaticidal; trypanoidal 4.0.0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-0000-00000-0000-0000-0000-00000  
Trypanosomiasis_, caused by the protozoa _Leishmania braziliensis_ and _Trypanosoma cruzi_, respectively, both belonging to the Trypanosomatidae family, class Kinetoplaseta. Treatments for such infections are expensive, so it has been estimated that controlling NTDs would require between USD 2 billion and USD 3 billion in funding over the next five-to-seven years [1; 2]. _Mucocutaneous leishmaniasisiasis_, caused by the parasite _L. braziliensis_, leads to the partial or total destruction of the mucous membranes of the nose, mouth, and throat. More than 90% of cases of _Mucocutaneous leishmaniasisensis_ occur in Bolivia, Brazil, Ethiopia, and Peru [3]. The use of chemotherapeutic, such as milletfosine, and pentavalent antimonials, such as \(N\)-methyl-glucamine antimoniate, is often the first step in the treatment of Leishmania infections [4]. Recent evaluations have shown increased resistance to antimonials in some endemic areas, limiting their effectiveness and demanding a more species-specific solution when possible [5]. Two pentavalent antimony products available in the US are sodium stibogluconate and meglumine antimoniate. The recommended dosage for both is 20 mg/kg/day for 28 to 30 days in mucocutaneous and visceral leishmaniasisis [6]. Chagas disease is caused by the protozoan _T. cruzi_ transmitted by the feces of triatimines, which are contaminated with metacyclic trypanastigotes and ejected by the insect after feeding [7]. _T. cruzi_ invades and multiplies as amastigotes within many different types of host cells, including muscle cells, macrophages, and fibroblasts [8]. Chagas disease is common in parts of Mexico, Central America, and South America, where an estimated 8 million people are infected [9]. Current options for the treatment of Chagas disease are restricted to benznidazole and nifurtimox, which are not well tolerated and imply frequent discontinuation of treatment [10]. In this scenario, there are essential oils (EOs) from several plant species with antiprotozoan properties that have become potential chemotherapeutic agents [11; 12]. EOs are insoluble in inorganic solvents (water) but soluble in organic solvents (ether, alcohol, fixed oils). They are volatile liquids, with a characteristic odor, and are widely used in the perfumery, aromatherapy, and cosmetics industry; they are also increasingly important in the pharmaceutical scene due to their wide range of applications and biological activities [13].