A Long Island state senator is being probed over claims that he improperly billed the state $18,500 for travel expenses.

The Nassau County DA’s Office is going over the ­records of GOP Sen. Carl Marcellino.

The inquiry is looking into whether Marcellino billed both taxpayers and his campaign committee for the same expenses from 2010 to 2013, according to NBC News 4.

During the period, Marcellino’s campaign committee was billed $20,000 in vehicle expenses. At the same time, the state reimbursed him $18,500.

Marcellino could not be reached for comment.