The simultaneous adsorption of poly(1-vinylpyrrolidone-co-acrylic acid) (PVcA) and sodium dodecyl sulfate (SDS) on positively charged alumina particles is carried out at pH 5.2 by measuring the amount of PVcA and SDS adsorbed, zeta potential, and sedimentation rate of alumina suspensions. In addition, conformation of PVcA and SDS adsorbed using their corresponding spin-labeled ones is estimated. The amount of PVcA adsorbed increases sharply and becomes a plateau with an increase of PVcA concentration, while a typical adsorption isotherm of SDS is obtained. In the simultaneous adsorption of PVcA and SDS under fixed initial concentrations of PVcA, the amount of PVcA adsorbed increases and reaches a maximum, and then decreases with SDS concentration. The enhancement in the adsorption is due to the interaction between SDS and PVcA as confirmed by surface tensiometry. The dispersion stability of alumina suspensions by the simultaneous adsorption of PVcA and SDS is considerably high compared with that by SDS adsorption alone. The high dispersion stability is due to the extended conformation of the adsorbed PVcA and the electrostatic repulsion force. Further, the mobility of SDS molecules in the PVcA-SDS adsorbed layer is found to be more restricted than that in the SDS adsorbed layer alone.