'Sanctuary' was never a huge hit for Syfy, it's season four premiere was watched by only 1.3 million viewers. Since its premiere in October, 'Sanctuary' has been steadily dropping in viewers, and season four is the lowest viewed season to date. The now series finale which aired on December 30, 2011 was watched by only 1.2 million viewers.
Here is the break down of the last five aired episodes:
Episode 09 - Chimera - November 29 - 0.95 million viewers
Episode 10 - Acolyte - December 9 - 1.50 million viewers
Episode 11 - The Depths - December 16 - 1.28 million viewers
Episode 12 - Sanctuary For None (Part 1) - December 23 - 1.11 million viewers
Episode 13 - Sanctuary For None (Part 2) (Series Finale) - December 30 - 1.28 million viewers