Three-dimensionally organized amide groups have been demonstrated to show a high sensitivity toward anionic guests using poly(phenylacetylene)s with L-leucine and amide functionalities (poly-PA-Leu). The poly-PA-Leu was prepared from the N-(4-ethynylphenylcarbonyl)-L-leucine ethyl ester (PA-Leu) using Rh+(2,5-norbornadiene)[(eta(6)-C6H5)B-(C6H5)(3)] (Rh(nbd)BPh4) as a catalyst. The biased helical conformation of poly-PA-Leu was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of ammonium salts including acetate, fluoride, benzoate, azide, and bromide (CH3COO-, F-. C6H5COO-, N-3(-), and Br-, respectively) into the poly-PA-Leu solution intensified the CD responses of the poly-PA-Leu, indicative of the polyacetylene helicity changes triggered by anion recognition of the amide groups. The efficient anion binding was observed for poly-PA-Leu with CH3COO-, whose apparent binding constant was estimated to be 1.1 x 10(3) (mol(-1).L). On the other hand, the anions including perchlorate (ClO4-), nitrate (NO3-), chloride (Cl-), and iodide (I-) had essentially no effects on both the CD and UV profiles of poly-PA-Leu. The guest specificity observed in the CD spectra of poly-PA-Leu with counteranions clearly correlated with the guest-basicity.