Go to your local hardware store or any other place that sells rat traps and purchase some of those rat traps and set them up with some cheese or bread and when the rat goes for the food they'll get killed.
You can also keep rats out of your house by making sure you keep crumbs and any other food cleaned up in your kitchen and keep the rest of the house clean.
Take out trash often as well.
Find any holes that the rats may be coming into your home through and cut up onions and place the onion slices in or near the holes and it will keep the rats away and out of your house.