The amplified antimicrobial activities of poly(arbutin) [poly(arb)] and its 10% octylated derivative [poly(arb)C8(10)] are described in this paper. Poly(arb) was prepared from monomeric arbutin via oxidative polymerization in an aqueous media, and poly(arb)-C8(10) was prepared by alkylation of poly(arb) with octyl isocyanate. The minimum inhibitory concentration of arbutin, poly(arb), and poly(arb)-C8(10) were determined to be 111, 15.2, and 52.6 mg/mL against Escherichia coli and 111, 1.00, and 1.00 mg/mL against StapHylococcus aureus, respectively. The higher antimicrobial activity of polymeric arbutin compared with monomeric arbutin was proposed to be the result of the neighboring effect of phenolic groups of polymers along with the concentration effect of the polymers on the surface of the culture plate, which was proved by ultraviolet-visible spectrophotometry.