Silver is an effective antimicrobial agent with low toxicity, which is important especially in the treatment of burn wounds where transient bacteremia is prevalent. In this research, the green method was employed to synthesis silver nanoparticles (AgNPs). The synthesized AgNPs were characterized using IR, XRD, DLS and UV/Visible Spectrophotometery. XRD pattern of AgNPs has a face‐centered cubic (FCC) form and crystalline lattice with a crystallite size of 12 nm. FT‐IR spectra indicate the functional groups of phytochemical compounds at Delonix regia extract DRE and AgNPs. DLS showed the distribution of average particle size of AgNPs that have 11 nm mean size of the particle. The prepared AgNPs were screened for their cytotoxic effect against colon carcinoma cells (HCT‐ 116 cell line), hepatic cellular carcinoma cells (HepG‐2) and breast carcinoma cells (MCF‐7). The cytotoxic effect of AgNPs is close to the cytotoxic effect of Doxorubicin standard drug. The toxicity of the AgNPs was tested on bacterial species such as Gm (+) positive bacteria (Bacillus subtilis) and Gm (‐) negative bacteria (Serrati amarcescence and Escherichia coli) and fungal species such as Candida albicans, Getrichm candidum and Aspergillus flavus. The antimicrobial activity of AgNPs was greater towards Gm (+) positive bacteria compared to Gm (‐) negative bacteria. These biological activities of the synthesized AgNPs could be promised to use it as a drug.