@Nordine011 , assuming that you are a US person ( citizen/GreenCard /Resident for Tax Purposes ), and since the taxes being levied by Belgium is based on value and not on rental. income, it is not in the character of income tax. Thus I would conclude that this tax is a tax on the property ( additional? ) and therefore put in as an expense under taxes . licenses, permits etc. on Schedule-E.
Is there more I can do for you ?