Yes you can, but I would make some other changes as well. It would also sound better to match the noun forms (you have both plural and singular possessive here). You could also use a pronoun like “that” or “what” to stand in for the noun phrase in a comparative construction like this, which might require another verb. And maybe “tuition” is a better (more specific) word than “cost of study”, because that’s probably what you really mean. So something like:
The tuition charged to domestic students is one third (of) that charged to international students.
Or more simply
The tuition is three times more for international students than domestic students.