This work aims at studying the structure of monomers on the dispersity of carbon black (CB) in a non-aqueous medium Isopar L. The polymethacrylate-grafted CB nanoparticles were prepared by a redox polymerization method. A series of methacrylate monomers containing alkyl side chain with different length and structure were employed for grafting. The structure and composition of polymethacrylate-grafted CB particles were characterized by a combination of FTIR, TGA and XPS. The particle size distribution, average diameter, contact angle to water and Isopar L and zeta potential of the prepared CB particles were investigated to provide insights into the effects of the monomer structure on the dispersity of modified CB particles in Isopar L. TEM images demonstrated that aggregation of modified CB particles reduced distinctly. The surface of CB particles changed from hydrophilic to hydrophobic after modification. Moreover, it is also found that the more branching or the longer the monomers used in the modification, the narrower the particle size distribution and the higher the zeta potential. The display prototype based on polymethacrylate-grafted carbon black particles showed an improved display performance under the electric field of 0.30 V μm−1. Especially, the EPD based on ethylhexyl methacrylate modified CB particles displayed the highest contrast ratio of 8.36 and minimum response time (527 ms) compared with the ones prepared with other modified particles.