Catalytic action of rare earth element, Ce(IV) to hydrolyzephosphomonoester bonds was confirmed. This effect wasconsidered to suppress abiotic synthesis ofnucleotides and nucleic acids in the primitive sea,and hence the origin of life. However, we found thatthe presence of proteins, especially albumin, stronglyinhibited the catalytic action of Ce(IV). Thisfinding was supported by preferential binding of rare earthelements (REEs) to proteins which was revealed using the radioisotopes of these REEs. Consequently, if a large amount ofproteins was synthesized in the primitive sea, abioticsynthesis of phosphomonoester compounds, and hencenucleic acids, might have been possible.