Peroxidase activities of RNAs containing 2'-amino groups, which were selected as aptamers binding to N-methylmesoporphyrin IX, were investigated. Some clones promoted the oxidation reaction of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with hydrogen peroxide (H2O2) in the presence of iron(Ill)protoporphyrin (hemin), whereas others did not. Each of them had a different substrate specificity. One of the active clones promoted the oxidation of o-dianisidine and beta -nicotinamide adenine dinucleotide reduced form (NADH) with H2O2 5 and 15 times faster than hemin only, respectively. On the other hand, one clone that was inactive on oxidation of ABTS exhibited the same level of activity on oxidation of o-dianisidine as that shown by the clone active on ABTS but no activity on NADH. By in vitro selection, we can produce various types of peroxidase-like non-natural RNAs.