Highlights • Novel rare-earth carboxylate compounds as corrosion inhibitors have been evaluated. • The yttrium 3-(4-methylbenzoyl)-propanoate acts as a mixed inhibitor after 24 h. • EIS and circuit models were used to evaluate the corrosion inhibition performance. • SEM/EDS shows a wide distribution of yttrium (Y) on the surface after immersion. Abstract In this work two novel rare-earth (RE) 3-(4-methylbenzoyl)-propanoate (mbp) complexes (RE(mbp) 3 ; RE = La, Y) have been investigated and compared with the well-researched inhibitor, lanthanum 4-hydroxycinnamate (La(4-OHcin) 3), for AS1020 mild steel in 0.01 M NaCl solutions. The electrochemical results reveal a high corrosion inhibition performance of Y(mbp) 3 which is attributed to the build-up of a protective surface film with a high level of corrosion resistance particularly after 24 h. Surface analyses indicate that the metal surface is protected during the immersion in Y(mbp) 3 -inhibited solutions and the presence of Y is confirmed on the substrate surface. [ABSTRACT FROM AUTHOR]