During an hour-long oral argument, several justices suggested the law violated free-speech protections of the First Amendment.
Justice Antonin Scalia said California's logic in banning videogame sales to minors could also apply to a ban on the sale of violent movies or books to children.
"Some of the Grimm's Fairy Tales are quite grim," Justice Scalia told an attorney for California. "Are they OK? Are you going to ban them, too?"
"What about films? What about comic books?" asked Justice Ruth Bader Ginsburg. "Why are videogames special?"
The court also questioned how the state could determine when violence in videogames was excessive.
The case has considerable implications for the videogame industry. Games rated as "mature," such as Activision Blizzard Inc.'s "Call of Duty" and Take-Two Interactive Software Inc.'s "Grand Theft Auto," are some of the industry's biggest sellers.