Catalysis is an essential concept in chemistry, playing a key role in industrial processes. Catalysis has been considered to be challenging not only for university students to comprehend but also for the teachers. In this Laboratory Experiment, we have described a simple activity for demonstrating the concept of catalysis using thread-based experiments for the first time. The chemical reduction using AgNO[subscript 3] as a metal source and NaBH[subscript 4] as a reducing agent was carried out to prepare silver nanoparticles (AgNPs). Then, the AgNP-loaded thread was fabricated by dropping the colloidal silver solution onto a knot of cotton thread. The continuous flow reduction of 4-nitrophenol (4-NP) in the presence of NaBH[subscript 4] was also carried out using the AgNP-loaded thread as a reactor. The capillary and gravitational forces led to a continuous flow of the reaction solution. A dramatic demonstration allows students to discover the catalysis with the naked eye, observing the color change of the reaction solution from yellow-green to colorless. At the same time, the catalytic conversion was analyzed with ImageJ software by processing the solution color captured with a smartphone camera under a homemade control lightbox. This activity is a novel approach to demonstrating the concept of catalysis. It presents a potential application of the thread-based experiment to related areas such as organic chemistry, forensic chemistry, and environmental chemistry.