A ribbon cassette capable of maintaining a position of one of its spools includes a shell, two spools, and two fasteners. Each of the fasteners is disposed at one side of one of the two spools for fastening the position of the spool. Therefore the spool is not able to rotate. Accordingly, the ribbon cassette is capable of preventing the spool from unexpected rotation during transportation. Therefore the ribbon is prevented from being driven by the spool. Hence the problem that the ribbon is slackened or is driven to protrude outside the ribbon cassette is solved.