Yes, THEOLOGY is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, E 1, O 1, L 1, O 1, G 2, Y 4.

Is it a valid word?

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

the rational and systematic study of religion and its influences and of the nature of religious truth
a particular system or school of religious beliefs and teachings
the learned profession acquired by specialized courses in religion (usually taught at a college or seminary)

Also: theological system.