A green synthesis of silver nanoparticles was developed, using a low-toxic system of microemulsion and nano emulsion with castor oil as the oily phase, Brij 96 V and 1,2-hexanediol as the surfactant and co-surfactant respectively. Geranium (P. hortorum) leaf aqueous extract was employed as a reducing agent. The content and concentration of a metallic precursor and geranium leaf extract (GLE) in the systems used makes it possible to obtain different sizes of silver nanoparticles from 25 to 150 nm. The characterization by FTIR and Z potential shows that the biomolecules of the plant extract act as a reducing and capping agent, giving negative charges to the nanoparticle surface. The present study represents a contribution to the green synthesis of silver nano particles that can be extended to other metals.