Is a polar bear prey to anything?

The polar bear has no actually prey but some polar bears have been known to have been killed bye killer whales and Greenland sharks. Sometimes there has been the polar bear preying on them!!!

Small cubs are preyed on by adult polar bears. Humans are pretty much the only other real issue. They can and do hunt polar bears. This is the reason their population went down many years ago to dangerously low levels. The limits on hunting allowed them to regain population.