Interpolymer complex formations between Form II helical poly (L-proline)[(PLP(II)] and Form I helical poly(L-proline)[PLP(I)] and poly(carboxylic acids) such as polyacrylic acid(PAA), atatic polymethacrylic acid(at-PMAA), and syndiotatic polymethacrylic acid( st-PMAA) have been studied by FT-IR X-ray diffraction, and light scattering measurements. It was found that the interpolymer complexes were formed via hydrogen bonding. The helical PLP(II)) formed polymer complex more favorably with PAA and at-PMAA having a disordered structure than wih st-PMAA having a ordered structure. In contrast, the helical PLP(I) formed polymer complex more favorably with st-PMAA than with PAA and at-PMAA. In addition, PLP(II) helix was destroyed on the complexation with PAA and at-PMAA, but the PLP(II) helix was perserved on the complexation with st-PMAA. However, the PLP(I) helix was all perserved on the complexation with poly(carboxylic acids). These findings could be explained in terms of molecular conformation of the complementary polymers associated with the complex formation.