A simple, rapid, and sensitive colorimetric assay for ascorbic acid (AA) was developed based on poly(methacrylic acid)‐stabilized silver nanoclusters (PMAA‐AgNCs). The AgNCs were prepared via a single‐step synthesis exploiting PMAA as both a reducing agent and a stabilizer. The sensing capability of this method is based on the color change associated with the growth in size of AgNCs, which turn into nanoparticles, resulting from the reduction of free Ag+ present in AgNCs solution to Ag0 by AA. In the presence of AA, an apparent surface plasmon resonance absorption peak of the silver nanoparticles was observed at 430 nm, and its intensity increased linearly with AA concentration, so that a solution color change could be observed with the naked eye. The proposed method exhibited a linear working concentration range of 0.25–100 μM and a detection limit of 95 nM. The sensor was employed to determine AA concentration in fruit juice and vitamin C tablet samples, affording results of high accuracy.