Your millage rate should not be higher on a rental property. As you said, your rate has gone from 4% to 6% which, in my opinion, is extremely unfair. It causes the landlord to have to raise rents above what they would be and that does not help anyone. That is a political problem though and has nothing to do with your real question. What has likely happened is some special measure was passed that increased it. That can happen from time to time if, for instance, they put a sidewalk in. You may be required to "contribute to the cause". There may be some increases that have been slipped in since you lived there. The best thing you can do is to call the tax assessor and ask them why the millage rate has increased and when it is expected to decrease, which will likely be never. Without seeing your statements, that question can't be answered. Call them. They will explain it to you and if it is wrong, they will fix it if you request it.