Targeting poorly water-soluble drugs to designated sites by exploiting their nanoscale structures provides a fateful opening for better drug delivery platforms. Microemulsions (μEs) are used as efficient reactors, due to their auxiliary flexibility, to produce functional nanoparticles of various chemical properties, shapes and sizes. In this study, a flexible oil-in-water (o/w) μE holding N-butyl acetate/Tween 20/lecithin/2-butanol/water was developed for the encapsulation and nanostructuration of Irbesartan (IBS), an antihypertensive agent. A pseudoternary phase diagram was delineated at a fixed surfactant/cosurfactant proportion set to limit the presence of a single-phase isotropic region for the as-formulated μE. In the optimal μE formulation consisting of “N-butyl acetate (15.0%), Tween 20-lecithin (20.0%), 2-butanol (30.0%) and water (35.0%)”, the IBS has a good solubility of about 3.5wt% at pH4.7. Micrographs of as-formulated IBS-free and IBS-loaded μE, analyzed by scanning electron microscopy (STEM), demonstrated the fine monomodal collection of spherical nanoparticles which remained stable for a half year of storage. Fourier transform IR studies showed good compatibility of IBS with μE excipients. However, the dynamic light scattering (DLS) revealed a growth in the mean particle size of the μE when stacking the drug, suggesting the appropriation of IBS in non-polar microenvironment, which was indorsed by fluorescence measurements. In addition, lyophilized non-aggregated nanoparticles of Irbesartan (IBS-NPs) were prepared, perceiving long-term stability, amorphous morphology, and enhanced dissolution rate that could be vital for the targeting mechanism of the nanodrugs.