Leishmania donovani, an obligate intracellular parasite of genus Leishmania causes visceral leishmaniasis that affects millions of people worldwide, especially in the Indian subcontinent and East Africa. Generic pentavalent antimonials have been the mainstay for therapy in the endemic regions due to efficacy and cost effectiveness but the growing incidence of their resistance has seriously hampered their use. This study discloses strong in vitro antileishmanial activity of 2-methyl-5 -(3'-methyl-but-2'-enyloxy)-[1,4]naphthoquinone (1), a prenyloxy-naphthoquinone isolated and characterised from roots of the plant Plumbago zeylanica (family-Plumbaginaceae). The observed EC50 for the compound 1 against promastigote and amastigote forms of L. donovani was significantly (p<0.001) lower than miltefosine, a reference drug. In context to limited treatment options and growing resistance for available drugs, compound 1 offers a greater prospect towards antileishmanial drug discovery and development.