The antibacterial activity of silver nanoparticles (AgNPs ) is well documented. AgNPs have a broad spectrum activity against gram negative and gram positive bacteria. Most reports evaluated the antibacterial activity of AgNPs in suspensions and not in clinically relevant vehicles such as hydrogels. In this work we prepared a library of monodispersed AgNPs with various sizes and we described the successful incorporation of these nanoparticles into two type of hydrogels: Carbopol ( represented anionic polymer ) and Pluronic ( represented nonionic polymer ). AgNPs exhibit excellent colloidal stability in both hydrogels upon storage. However, aggregation occurred upon contact with Tryptic soy agar ( bacterial growth media ) for carbopol hydrogels but not for pluronic hydrogels. AgNPs showed different antibacterial activity in both hydrogels, with a common trend supported higher activity for AgNPs with smaller size. This work highlighted the importance of considering nanoparticles size and the type of gelling agent when formulations AgNPs hydrogel which affect their colloidal stability and antibacterial activity.