Amos was a contemporary of Hosea, Micah, and Isaiah and prophesied during the reigns of King Uzziah of Judah (791-740 BC) and Jeroboam II of Israel (793-753 BC). Within this time frame (790-750 BC), it is not possible to say exactly when Amos went to Israel. Though there is a reference to a well-known and historic earthquake (Amos 1:1; Zechariah 14:5), we do not know the exact date of this event, though scholars estimate it to be 760 BC.1 Traditionally the book is assigned to the middle or later years of the reign of King Jeroboam II, perhaps just before his death (753 BC).2
1 The words of Amos, who was among the shepherds of Tekoa, which he saw concerning Israel in the days of Uzziah king of Judah and in the days of Jeroboam the son of Joash, king of Israel, two years before the earthquake.