No, the Constitution does not mention how many justices must serve on the U.S. Supreme Court. The Judiciary Act of 1789, provided for a Chief Justice and five associate justices. In 1801, a new law provided that the Supreme Court would consist of one chief justice and four associate justices. In 1807, the number of associate justices was set at six. In 1837, there were eight associate justices. In 1864, Congress changed the number of associate justices to nine, meaning there were a total of ten Supreme Court justices (nine Associate Justices and the Chief Justice). In 1869, Congress passed a law setting the number of associate justices at eight. Since that time, there have been nine Supreme Court Justices.