Silver nanoparticles have been synthesized using AgNO3 as the metallic source and onion-type multilamellar vesicles (MLV) as the microreactor, where the Genamin T020 organic component is acting as the reductant. Silver ions were introduced into MLV either by diffusion from the dispersion medium, or directly by mixing AgNO3 solution with Genamin T020 followed by a shear process. Both the effect of synthetic routes and aging upon the nanoparticle size and assemblies are studied by TEM. In the former case, the size of silver nanoparticles increases from ca. 3 nm to 9.6 nm with increasing dispersion time (30 min and 17 h respectively). For short dispersion times, silver nanoparticles assemble in circular aggregates. The typical size of those aggregates resembles that of MLV, thus indicating an in-situ synthesis. In the latter case, nanoparticle growth is quicker: 7-8 nm silver particles being synthesized in 30 min. Nanoparticles arrange themselves then in parallel strings separated from each other, forming planes, stacked on each other in some cases. A higher onion internal pH measured by P-31 NMR is assumed to induce Ag2O precipitation inside onions contributing to Ag(I) reduction in metallic nanoparticles.