Which one is right, faculty of science Or faculty of sciences? I think "sciences" is better as it refers to multiple departments.
One form isn't necessary more correct than the other; you'll find some institutions that use one and other institutions that use the other, and many others that use both— or neither.
Science in the broad sense of the system of knowledge developed and organized through the scientific method is not countable, but like most non-count nouns in English, it can be used as a count noun. Individual branches of sciences are known as the sciences, much in the same way that a bakery can have a selection of breads in its selection of bread, and you discover many truths in the pursuit of truth.
If an institution perceived science as a particular branch of knowledge, it might well organize all science and related disciplines in a Faculty (or School or Department or Division or College etc.) of Science. You can find examples of them all around the world: the National University of Singapore, the University of Sydney, the University of Regina, the University of St. Andrews, the Massachusetts Institute of Technology and so on.
But other institutions might prefer to treat sciences as related but independent disciplines, taking a plural, and thus have a Faculty of Sciences, as do Singapore Polytechnic, University of Adelaide, the University of Quebec at Montreal, the University of York, or North Carolina State University.
Neither form is globally preferable, although there may be some regional patterns. Indeed, some institutions use both forms; the University of Auckland has, on the one hand, a Faculty of Science, but additionally, a Faculty of Medical and Health Sciences.
The same point can be made for the use of Faculty of Art vs. Faculty of the Arts (although arts is a slippery term, as very often in education it refers to the liberal arts, not the fine arts).
I prefer "faculty of the sciences", like "faculty of the humanities".