The optimization of silver nanoparticles synthesis for colorimetric sensing has been done to result in silver nanoparticle stability. It includes the mole concentration of AgNO3 as a resource of AgO and sodium borohydride as a reducing agent of silver nitrate. The result of AgNp use to colorimetric sensing of cortisol. The stability of AgNp was evaluated by UV-Vis spectroscopy, Particle Size Analyzer (PSA), and Fourier Transform Infrared Spectroscopy (FTIR) method. The colorimetric sensing by silver nanoparticles has been successfully developed with the color solution change from yellow to orange-pink when interacting with cortisol. The best optimization of silver nanoparticle synthesis is 1.O mM of silver nitrate concentration and 3 mM of sodium borohydride concentration with the size of silver nanoparticles size is 15.23 nm and 13.48 nm, respectively.