The formation mechanism of helical polyacetylene (H-PA) in chiral nematic liquid crystal (N*-LC) used as an asymmetric reaction field was investigated by taking into account the relationship in morphology between the H-PA and N*-LC. The spiral texture characteristic of N*-LC observed in polarized optical microscopy was examined and compared with the spiral morphology of the resultant H-PA. The distance between the fibril bundles of H-PA was determined to be half of a helical pitch of N*-LC; in addition, the helical axis of H-PA is orthogonal to that of N*-LC. Interestingly, the screw direction of the H-PA fibrils was found to be opposite to that of N*-LC. On the basis of these experimental facts, we propose a chemically graspable formation mechanism of H-PA in N*-LC.