Yes, MAINTENANCE is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, I 1, N 1, T 1, E 1, N 1, A 1, N 1, C 3, E 1.

Is it a valid word?

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

activity involved in maintaining something in good working order
means of maintenance of a family or group
court-ordered support paid by one spouse to another after they are separated
the act of sustaining life by food or providing a means of subsistence
the unauthorized interference in a legal action by a person having no interest in it (as by helping one party with money or otherwise to continue the action) so as to obstruct justice or promote unnecessary litigation or unsettle the peace of the community

Also: criminal maintenance.

Not playable in Scrabble US: SUSTAINMENT.