Yes - tea tree oil can kill roaches. The chances of successfully using tea tree oil to kill roaches are slim, though. It is not a simple case of spraying a surface, and a roach dies if it walks on it. You would have to hit the cockroach directly with lots of tea tree oil to work. For that reason, I would not be using tea tree oil to kill roaches in my home was infested. I would use it as a deterrent, though.