Virtually everything associated with operating, insuring, protecting, repairing, or managing investment real estate can be deducted as an expense.
Some items that add to the property or extend its life, such as a new roof or a building addition, cannot be deducted. Instead, you have to depreciate them a little bit each year.
This is an area that might require some accounting assistance.
For a general overview, read IRS Publication 527, “Residential Rental Property,” and Publication 946, “How to Depreciate Property,” for more details. They are available at www.irs.gov to download, or by calling 800-829-1040 to request a mailed copy.