Infrared spectroscopy was used to study the interpolymer complexation of poly(acrylic acid) with polyacrylamide. The spectrum of the interpolymer complex showed characteristic absorption bands which are different from those of the spectra of the individual components, particularly in the O-H and N-H stretching vibration regions. The effects of ionic strength and poly(acrylic acid) weight fractions on the spectral features of the complex were investigated. It was found that hydrogen bonding is the primary mechanism of interaction between the two polymers.