The interpolymer interaction, morphology and chain dynamics of the poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complex are examined by using C-13 CP/MAS n.m.r. methods. By analysing C-13 CP/MAS spectra of the complex we conclude that there exist three hydrogen bonding forms for the carboxyl group of PAA, namely : (1) the complex form, interpolymer hydrogen bonding between PEO molecules; (2) the dimeric form, intrapolymer hydrogen bonding within PAA molecules; and (3) the free form, no particular form of hydrogen bonding. The morphology of the complex is investigated by the H-1 spin-lattice relaxation time in the laboratory frame (T-1), and that in the rotating frame (T-1p). We found that the domain sizes of the three hydrogen bonding forms of PAA are less than a few tens of angstroms, and the PAA/PEO complex is miscible on a molecular level. Further, temperature dependence of C-13 linewidth (T-2) is examined to study effects of complexation on the molecular motion of the component polymers. The temperatures at which the maximum linewidths are observed for the main chain carbon of PEO and PAA in the PAA/PEO complex are 310 and 362 K, respectively. This indicates that the motional heterogeneity is present in spite of a single T-g for the PAA/PEO complex. Further, we discuss the structural difference between the poly(methacrylic acid)/PEO complex and the PAA/PEO complex.