Abstract: A method for preparing a biogenic guanidine complex, the method including: mixing dimethyl sulfoxide (DMSO) with water in a volume ratio thereof of 1:1 to yield a solvent DMSO-H2O; adding organic guanidine (G) and a compound MX2 in a molar ratio G/MX2=1:1 or 2:1 to the solvent DMSO-H2O, where the organic guanidine (G) is selected from arginine (Arg), guanidinoacetic acid (Gaa), creatine (Cra), creatinine (Cran), guanine (Gua), and agmatine (Agm); M represents Fe2+, Mg2+, or Zn2+; and X represents Cl?, CH3COO?, or CH3CH(OH)COO?; stirring the solvent DMSO-H2O containing the organic guanidine and the compound MX2; recycling the solvent DMSO-H2O through vacuum distillation and obtaining a solid; transferring the solid to a Buchner funnel, and washing the solid with deionized water and ethanol consecutively; and removing the deionized water and ethanol through vacuum filtration, and drying the solid.