New high-performance composites with high thermal conductivity, good flame retardanc-y, and low dielectric loss using cyanate ester (CE) resin as the matrix and hybrid fillers consisting of aluminum nitride (AlN) and multiwalled carbon nanotubes (MCNTs) as the functional phase were developed. In addition to the original fillers, surface-treated MN (kAlN) and MCNTs (eMCNTs) were prepared to develop four types of hybrid fillers and the corresponding composites. The structures and properties of the ternary composites can be adjusted by controlling the interaction between the nanotubes and the AN. Both AlN and kAlN fillers can improve the dispersion of nanotubes in the CE resin, regardless of whether the nanotubes are modified, whereas only eMNCTs can improve the dispersion of AlN or kAlN in the matrix. The kAlN-eMCNT hybrid was found to have the highest synergistic effect, endowing CE resin with outstanding thermal conductivity, low dielectric loss, significantly improved processing characteristics, and flame retardancy.