2020 Chartarrayawadee et al., published by De Gruyter 2020. The Lysimachia foenumgraecum Hance extract (LHE) was used for silver nanoparticles (AgNPs) synthesis. In this study, the herbal plant of Lysimachia foenumgraecum Hance (LH) was extracted with deionized water and we are the first to successfully use LHE as reducing and stabilizing agents for the green synthesis of AgNPs. The concentration of LHE used in this study was in the range of 0.003 to 1.0 wt%. Aqueous colloidal solutions of AgNPs reduced and stabilized by LHE show long-term stability due to the steric stabilization effect. This can be confirmed by zeta potential measurements which afforded values approximately of 0 mV, indicating the steric stability of AgNPs colloidal solutions synthesized by LHE. Furthermore, the obtained AgNPs colloidal solutions show superior antibacterial effect to gram-positive bacteria (Staphylococcus aureus) comparing to Chloramphenicol (positive control). AgNPs with LHE 0.003 wt% affords the highest antibacterial effect to S. aureus showing an inhibition zone diameter of 19.08 ± 0.67 mm; which is superior to Chloramphenicol.