The colorimetric detection of dopamine was investigated to enhance the dopamine detection sensitivity. The detection was through the oxidation of AgNPs by hydrogen peroxide converted from dopamine along with dihydroxyphenylacetaldehyde. The conversion was facilitated by monoamine oxidase-Bs (MAO-Bs) bound to biomimetic membranes. The absorbance at 410 nm decreased with the increase in dopamine concentration. The limit of detection was determined to be 0.013 μM for 0.01 to 3.5 μM dopamine in the linear range of absorbance. The absorbance change corresponded to the conversion of Ag to Ag2O, which occurred with the hydrogen peroxide released through MAO-Bs from dopamine. These results indicate that the AgNP degradation based on the immobilized MAO-Bs is sufficiently appropriate for the high-sensitivity absorbance detection of dopamine with a wide linear range.