PURPOSE: To obtain a substituted hydrazinocarbonyl group-containing high- molecular compound forming a stable complex compound with a heavy metal, especially, uranium, and having excellent selective adsorptivity therefor, by (co)polymerizing a specified vinyl compound.

CONSTITUTION: A high-molecular compound containing an acid chloride group, an acid anhydride group or an acid amide group is reacted with a compound of formula I (wherein M is H, Na, or K) to obtain a vinyl compound of formula II(wherein M is H, Na, or K, and R is H or CH3), e.g., 1-methacryloyl-2-oxalo- hydrazine. A (co)polymer obtained by polymerizing the vinyl compound or copolymerizing it with other monomers (e.g., divinylbenzene) is hydrolyzed with an alkali or the like to obtain a substituted hydrazinocarbonyl group-containing high-molecular compound containing groups of formula III. This compound, if desired, after processing into staple or a net, is placed in, for example, a column or a tower and contacted with an aqueous solution containing heavy metals.