Hydrogen peroxide (H2O2) is a type of reactive oxygen species widespread in biological tissues. It is an important biomarker of oxidative stress, cancers, asthma, etc. In this regard, development of precise and cost-effective sensors for detection of H2O2 in vitro and in vivo is of great significance for biomedicine. In this paper, a colorimetric method is introduced for sensing hydrogen peroxide using tyrosine-stabilized silver nanoparticles. In aqueous solutions, the colorimetric method demonstrated a linear range of 0.4–5 μM with a detection limit (LOD) of 150 nM, whereas in human blood serum the linear range was within 0.7–20 μM characterized by a LOD of 250 nM. Recovery tests in blood serum yielded results within the acceptable range 96–101%, confirming the method's accuracy and reliability. Possible mechanisms of silver nanoparticles/nanoclusters interaction with H2O2 during its detection were examined using fluorescence spectroscopy and dynamic light scattering methods.