Synthetic polymer ligands (PLs) that recognize and neutralize specific biomacromolecules have attracted attention as stable substitutes for ligands such as antibodies and aptamers. PLs have been reported to strongly interact with target proteins and can be prepared by optimizing the combination and relative proportion of functional groups, by molecular imprinting polymerization, and/or by affinity purification. However, little has been reported about a strategy to prepare PLs capable of specifically recognizing a peptide from a group of targets with similar molecular weight and amino acid composition. In this study, we show that such PLs can be prepared by minimization of molecular weight and density of functional units. The resulting PLs recognize the target toxin exclusively and with 100-fold stronger affinity from a mixture of similar toxins. The target toxin is neutralized as a result. We believe that the minimization approach will become a valuable tool to prepare "plastic aptamers" with strong affinity for specific target peptides.