Objective: To develop and characterize Piper retrofractum extract loaded nanostructured lipid carriers (PRE loaded NLCs) for topical oral cavity administration to enhance bioavailability and stability of piperine.Methods: PRE loaded NLCs were prepared with a hot high-pressure homogenization technique followed by coating the particle surface with mucoadhesive polymers; polyethene glycol 400 (PEG) and polyvinyl alcohol (PVA). The physicochemical properties in terms of particle size, polydispersity index, zeta potential, drug entrapment efficiency, in vitro drug release profile and antimicrobial activities were examined. In vitro, mucoadhesion studies were assessed by the wash-off test. The physicochemical stabilities of mouth spray containing PRE loaded NLCs were investigated by kept at room temperature and 4 °C for 6 mo. Results:The PRE loaded NLCs showed spherical shape with a mean particle size of ~100-120 nm and zeta potential of ~-24 mV. Up to 90% drug entrapment efficiency was achieved. PEG-NLCs and PVA-NLCs showed a strong interaction with porcine buccal mucosa than uncoated-NLCs. All PRE loaded NLCs formulations revealed fast release characteristics and effective against Streptococcus mutans and S. sanguinis. The mouth spray containing PRE loaded NLCs showed good physical stability without particle aggregation. In addition, the chemical stability of piperine in NLCs was significantly improved during storage at both storage conditions compared to its solution form. Conclusion:The developed PRE loaded polymer coated-NLCs showed high potential to use as a local drug delivery system for reducing the bacterial growth in the oral cavity.