Is it ethical to host ads on an institute provided homepage? I am affiliated to an institute and they provide each student an opportunity to make their own homepage, which they can put up as www.[institute-webpage]/[username]. Now, this webpage is not reviewed by the institute. I made my homepage recently and I am wondering if it is ethical to put ads on it. 

On one hand, it is my own website, while on the other hand, it is hosted on their server and I don't have to pay anything to get this.
It may depend on the rules of your institute, but I'd bet that putting ads on your homepage is not allowed.  You should certainly not put up ads without verifying that you have official permission to do so.

If you work at a public university or other governmental institute, then putting up ads could be considered using government property for personal gain.  That's probably not just unethical, but illegal (but you'd have to look into the appropriate laws in your jurisdiction to be sure).

If you work at a private university or institute, then it may not be illegal, but there are still probably institute rules against using institute property in this way.  I'd be surprised if any big organization didn't have such rules.