The comb‐like styrene‐maleic anhydride copolymer‐g‐isatoic anhydride‐methoxypolyethylene glycols condensate (SMA‐g‐IA‐MPEG) was synthesized by transesterification and amidation reaction. The chemical structure of SMA‐g‐IA‐MPEG was characterized by FTIR and 1H‐NMR. The comb‐like modified SMA was first employed as the dispersant of disperse dyes suspension in this paper. The addition of SMA‐g‐IA‐MPEG dispersant improved the dispersibility and stability of the disperse dyes suspension observably due to the steric hindrance and electrostatic repulsion on the surface of dye particles. The impacts of the length of side chains on the particle size, Zeta potential, centrifugal stability, and temperature sensitivity of disperse dyes suspensions were particularly discussed. The results showed that SMA‐g‐IA‐MPEG with moderate length of side chain had the best dispersibility for disperse dyes suspension and the average particle size of dyes can be reduced to 356.1 nm. Thus, the comb‐like dispersants played a vital role in dispersing of disperse dyes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47330.