Major purpose of this study was to investigate the effect of two temperatures of 37°C and 50°C on biosynthesis of extracellular silver and gold nanoparticles by some bacteria. To perform biosynthesis of nanoparticles, the bacterial culture supernatants of Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Bacillus cereus, Escherichia coli, Klebsiella pneumonia and Yersinia enterocolitica were treated with aqueous solutions of silver nitrate (25 µL of 1 M) and gold III chloride ions (25 µL of 1 M) and incubated in shaker incubators (at 150 rpm) at 37°C and 50°C. Nanoparticles of silver and gold in the culture were monitored through UV-visible spectrophotometry and confirmed by X-ray diffraction analysis (XRD). The average size and morphology of nanoparticles were determined by transmission electron microscopy (TEM). The results obtained indicated that silver and gold nanoparticles were produced in the bacterial culture supernatants within 24 hr and the rate of production was relatively more at 50°C. XRD analysis confirmed biosynthesis of nanoparticles and UV–visible spectra showed maximum absorption for silver and gold nanoparticles at 410-430 and 510-540 nm respectively. In addition, TEM images illustrated the average size of nanoparticles from 10 to 80 nm. Overall, biosynthesis of nanoparticles is a simple method and does not require more time. In addition, some bacterial stains could produce reductive enzymes for reduction of silver and gold ions and this bioreduction could be affected by temperatures.