A high-spin polyradical, poly {[4-(dianisylaminium)phenyl]acetylene} 1(+), was synthesized as a pi-conjugated polymer with an excess of the one-handed helical structure bearing stable aminium cation radicals. [4-(Dianisylamino)phenyl]acetylene (3) was synthesized and polymerized using [Rh(norbornadiene)Cl](2) in (R)-1-phenylethylamine, (S)-1-phenylethylamine, or triethylamine to produce the corresponding poly {[4-(dianisylamino) phenyl]acetylene} 1 (1((R)-PEA), 1((S)-PEA), and 1(TEA)). The positive and negative Cotton effects were observed at 270-450 nm for the polymers 1((R)-PEA) and 1((S)-PEA), indicating that an excess of the one-handed helical polyacetylene backbone was induced by the polymerization using chiral solvents despite the achiral monomer. The oxidation of 1 with NOPF6 gave the corresponding aminium polyradicals 1(+), and the circular dichroism (CD) spectrum was observed even after the oxidation of the helical polyradical 1((R)-PEA)(+). The SQUID and NMR shift measurements indicated a high-spin state of the polyradical at room temperature and a contribution of the well-regulated helical structure to the through-space interaction between the aminium cation radicals.