Citrate-stabilized silver nanoplates (AgNPs) were prepared using a seed-mediated growth method. The AgNP shape and size were controlled using potassium permanganate (KMnO4) as an oxidant and ascorbic acid (AA) as a reductant. Using KMnO4, 42 nm nanoplates were changed to 22.9 nm nanodisks because of the release of silver ions. Using AA, the oxidized AgNPs were resynthesized to their initial plate form. These results are similar to those obtained using photoinduced shape control of silver nanoparticles; however, the chemical oxidation/reduction method can control the shape of AgNPs, both quantitatively and reversibly. In addition, because of redox-related visible spectral changes, solution color varies with AgNPs size. That feature may be useful in various applications.