The cause, location and date of the British actor's death were not immediately reported.
"This is a post we never thought we would have to write," his webpage said under the heading "Tragic News."
"It is with great sadness that we have to announce the sudden and unexpected passing of Robin Sachs," the message said.
"Please join us in raising a glass to Robin -- goodbye, dear friend. Thank you for all the laughter and the cookies. We will miss you so very much."
In addition to playing Ethan Rayne, nemesis of Anthony Head's watcher character Giles on "Buffy," Sachs also appeared in TV's "Torchwood: Miracle Day" and the films "Ocean's Eleven," "Galaxy Quest" and "Jurassic Park: The Lost World."