PURPOSE: To recover uranium efficiently from plankton, by subjecting concentrated and dehydrated plankton to methane fermentation treatment, separating uranyl satls contained in the plankton as soluble ammonium complex salts of uranyl carbonate.

CONSTITUTION: Collected plankton is concentrated by pressure floatation method, etc. and dehydrated by a centrifugal separator. The prepared concentrated caky plankton is subjected to methanol fermentation treatment, so that uranyl salts contained in the plankton are converted into soluble ammonium complex salts of uranyl carbonate. Many other substances contained in it are converted into chlorides, carbonates, hydroxides, and sulfides, and they are soldified, made into a dehydrated cake by a centrifugal separator, etc. and removed. The uranyl complex salts contained in the filtrate are concentrated to give the desired recovered uranium solution. Methane recovered by methane fermentation is used as an energy source necessary for the process.