By taking advantage of the powerful oxidation property of hypochlorite (OCl-), we developed a solid-phase colorimetric sensor for the detection of OCl- based on 13 nm AuNPs immobilized on a 3-aminopropyltriethoxysilane APTES-coated substrate. This colorimetric sensor utilizes the aggregation and anti-aggregation properties of AuNPs arising from the interaction between dithiothreitol (DTT) and OCl-. When the amount of OCl- increases, the color of the substrate changes from blue to red, allowing for naked-eye detection at concentrations as low as 2.48 μM within the reaction time of 5 minutes. Unlike conventional solution-based colorimetric sensors that can be easily affected by ionic strength, pH values, and temperature, this solid-phase sensor shows a more stable detection performance. Additionally, this solid-phase sensor can be further miniaturized, providing high availability and durability for use in daily life.