Yes, BUFFALOS is a Scrabble word!

Letter values in Scrabble US: B 3, U 1, F 4, F 4, A 1, L 1, O 1, S 1.

Is it a valid word?

BUFFALOS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

large shaggy-haired brown bison of North American plains
a city on Lake Erie in western New York (near Niagara Falls)
meat from an American bison
any of several Old World animals resembling oxen including, e.g., water buffalo; Cape buffalo

Also: american bison, american buffalo, bison bison, old world buffalo.