Chitosan nanoparticles are nontoxic polymers with diverse biomedical applications. Traditional nanoparticle synthesis often involves harmful chemicals or results in reduced desirable properties, sparking interest in green synthesis methods for nanoparticle production. Utilizing plant-based phytochemicals as reducing and capping agents offers advantages like biocompatibility, sustainability, and safety. This study explored Blumea balsamifera leaf extract for chitosan nanoparticle (CNP) synthesis. CNPs were synthesized using pH-induced gelation and characterized by DLS and SEM. B. balsamifera extract, prepared using ethanol, achieved a total phenolic content of 19.37 ± 6.35 mg GAE/g dry weight. DLS characterization revealed a broad size distribution, with an average particle diameter of 908.9 ± 93.6 nm and peaks at 11.11 ± 0.97 nm, 164.45 ± 6.13 nm, and 1672.04 ± 338.75 nm. SEM measurements showed spherical particles with a diameter of 56.8–63.0 nm. UV-Vis analysis, with an absorption peak at 286.5 ± 0.5 nm, was used to optimize CNP biosynthesis through a Face-Centered Central Composite Design (FCCCD). Higher concentrations of B. balsamifera extract (0.05 g/mL) and chitosan (19.1 mg/mL) maximized nanoparticle yield with a mass of 100 μg/mL. Antibacterial testing against E. coli demonstrated a minimum inhibitory concentration of 25 μg/mL. B. balsamifera extract effectively synthesized nanochitosan particles, showing potential for antibacterial applications.