This paper presents a method of purification with Amberlite IRC-50 of the sample solution containing 4-9 μg/ml of vitamin B_<12> as the final step of a series of processes for the preparation of vitamin B_<12> crystal. Almost all vitamin B_<12> contained in the sample solution which had been poured onto IRC-50 resin column was adsorbed forming a red band. The liquid chromatogram obtained by the elution with 0.1 N HCl-75% acetone showed that the majority of impurities adsorbed on the resin was eliminated in earlier fractions and that vitamin B_<12> solution of high purity could be obtained when appropriate fractions were collected. The vitamin B_<12> solution which had passed through Amberlite IR-4B resin column for the purpose of eliminating hydrochloric acid was evaporated under reduced pressure, followed by crystallization in aqueous acetone.