Provided are a barium-sulfate scale inhibitor and a barium-sulfate scale inhibitor composition each of which can express a high barium-sulfate scale-inhibiting ability. Also provided is a method of inhibiting a barium-sulfate scale that can express a high barium-sulfate scale-inhibiting ability. The barium-sulfate scale inhibitor of the present invention includes a sulfonic acid group-containing copolymer obtained by polymerizing a monomer composition containing a carboxyl group-containing monomer and a sulfonic acid group-containing monomer, in which when the barium-sulfate scale inhibitor is added at a solid content concentration of 1 wt % to high-salt-concentration water having a metal salt concentration of 10 wt % or more, the sulfonic acid group-containing copolymer is free from precipitating.
展开▼
