Ceria/poly(acrylic acid) microgel composite with anticorrosion potential has been synthesized via an in situ polymerization method. This polymer composite matrix has demonstrated significant reduction in API 5L X70 steel corrosion in 0.5 M HC1. In-depth studies of the anticorrosion properties of this microgel have been conducted by corrosion electrochemistry, and its adsorption on steel altered both anodic dissolution and cathodic hydrogen evolution in the acid medium. Increment of CeO2 content within the PAA/CeO2 hybrid composite improved its surface protective performance; 1 and 5 g of CeO2 within the composite recorded 82 and 90% inhibition efficiency, respectively, compared to PAA alone (62%), at equal concentration. PAA formed a protective polymeric film on steel upon molecular adsorption, but in the presence of the PAA/CeO2, the metal surface protection was enhanced by the adhesion of compact hybrid films. PAA/CeO2 microgel composite may have a future as an anticorrosive paint component for metal surface treatments.