Adsorption behavior of poly(acrylic acid) (PAA) and poly(vinyl pyrrolidone) (PVP) on alumina from their binary mixtures in aqueous solution at pH 5.2 has been studied by measuring the adsorbed amount of polymers, dispersion stability, and ESR spectra. The adsorption of PAA alone shows a strong affinity with a large adsorbed amount for alumina surface, but that of PVP alone is very weak and small. In fixed initial concentrations of PAA the adsorption of PVP is considerably enhanced, probably due to the interaction of PVP with PAA adsorbed on alumina through hydrogen bonding. From ESR spectra of spin-labeled PAA and adsorbed PVP, it is found that in the co-adsorption of PAA and PVP, adsorbed PAA takes predominantly trains, while PVP is mainly adsorbed in loops or tails. The stability of alumina dispersion has also been discussed from the conformation of polymers adsorbed on alumina.