AbstractSummary: Phosphorus compounds were employed as catalysts in Reversible Chain Transfer Catalyzed Polymerization (RTCP), a novel class of living radical polymerization (LRP) which we had recently developed. Low‐polydispersity polystyrene and poly(methyl methacrylate) with predicted molecular weights were obtained with a fairly high conversion in a fairly short time. These catalysts are particularly featured by their high reactivity hence small amounts being required, low toxicity, and low cost. Some phosphorus catalysts used in this work are among the least expensive catalysts/mediators of LRP developed so far.