This article describes the use of copolymeric dispersants with an acrylic backbone and phosphate side groups for formulating carbon black (CB)-epoxy composites. Six phosphate-modified acrylic copolymer dispersants were prepared from the corresponding epoxy-containing acrylic copolymers. The phosphate-modified dispersant with the highest concentration of hydrophobic alkyl chains and typical phosphate moiety groups showed a desirable passivation effect on the CB, and was found to lower the viscosity of the CB-epoxy paste, leading to the well-cured composite after heat treatment. The thick composite film prepared by employing the CB/phosphate-containing dispersant/ epoxy paste was built up on a Cu plate by a screen printing process followed by thermal curing. The dielectric properties of the 3.1 vol% CB-filled epoxy film showed a high dielectric constant (K 6280) and a rather low dissipation factor (Df, 61%)@ 1 MHz.