Mice are repelled by the scent of natural peppermint essential oil (also called "oil of peppermint"). To rid your house of rodents, simply put a few drops of peppermint essential oil on cotton balls and place them around the house, sprinkle the oil directly on some items, or make a scented spray with two teaspoons of peppermint essential oil per cup of water.
The peppermint applications will remain an effective repellent for as long as the scent remains. This varies according to conditions, of course, but you should get good results in most cases if you replenish the oil every two or three weeks.
Try to strongly scent areas where you think the mice might be entering or hiding out--like basements and stairs--as well as the areas you see them most.
The scent of peppermint oil drives mice away without the danger of poisoning pets and, as a bonus, creates a very pleasant atmosphere for human inhabitants.