BaTiO3 coated with polyaniline (PANI), forming a composite structure, were synthesized by in situ polymerization at different BaTiO3/aniline weight ratio (BaTiO3/Ani = 1/1, 1/2, 1/3) and introduced into epoxy resin to be a microwave absorber. The spectroscopic characterizations of the formation processes of BaTiO3/polyaniline (BaTiO3/PANI) composites were studied using Fourier transform infrared, ultraviolet–visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorption performances were investigated by reflectivity in 2–18 and 18–40 GHz using arch method. The results showed that a wider absorption frequency range could be obtained by adding different PANI content in BaTiO3.