Although there are a number of writings dating from as far back as the time of Moses, only thirty-nine compose the sacred and authoritative Old Testament canon. Moses penned the first five books, with the exception of the last few chapters of Deuteronomy that recount his death and burial. Other books were written by kings and prophets. The prophet Malachi wrote the final book of the Old Testament during the Persian domination in 430 B.C. After this time, no additional prophets brought messages from God to the Israelites. The Old Testament canon was complete and closed.
The oldest surviving document that lists the contents of the Old Testament canon comes from a Christian scholar named Melito of Sardis and is dated at A.D. 170.
Reference: The Everything History of the Bible Book, Jeffery Donley, Ph.D., Adams Media.