Study by chemical modification of Ser, Arg, His residues and sulfhydryl groups on bovine seryl-tRNA synthetase showed that Ser residues appeared to be unnecessary for the recognition mechanism, but Arg and His residues were essential. It was considered that different sulfhydryl groups related with each recognition of tRNA and ATP. Poly-arginine inhibited the interaction between serine tRNA and SerRS. The CD spectra of a mixture of serine tRNA and poly-arginine indicated that higher-order structure of tRNA changed. Furthermore, the Km and Vmax values of bovine serine isoacceptor, yeast serine tRNA and E. coli serine tRNA for bovine SerRS examined and it was discussed the differences of those base sequences.