Magnetic multiwalled carbon nanotubes (M-MWNTs) have been functionalized with mixed surfactants consisting of a sugar-based surfactant and an ionic surfactant. The synergistic effect of the two surfactants results in more surfactants adsorbed and the formation of a more disordered structure of assembled surfactants. These two aspects facilitate simultaneous hydrogen bonding and electrostatic interactions with proteins. It has been demonstrated that the M-MWNTs functionalized with mixed surfactants adsorbed more proteins than the M-MWNTs functionalized with single surfactants. The M-MWNTs functionalized with mixed surfactants have been tested for the adsorption of two proteins, bovine serum albumin (BSA) with a low isoelectric point and lysozyme with a high isoelectric point, and similar results have been obtained. Hence, carbon nanotubes functionalized with mixed surfactants have a wide range of potential applications for protein adsorption.