Yep, just like Jynelle said- they have to be kept in pairs. Otherwise, they will become depressed and have a high chance of developing behavorial problems. You also want to get the biggest cage you can afford, they have to be kept in a cage no smaller than a guinea pig cage. Hamster and gerbil cages are way to small. Be sure the cage has levels so they have more room to play.

Also, do not use commerical rat food such as Kaytee. They are not formulated with rats nutrional needs in mind. There is corn in commerical rat foods which harbors fungus which is dangerous to rats. There is also a chemical called ethoxyquin in a lot of commerical diets, which causes cancer in humans- why would you want to feed that to your rats? Suebee's Mix is an awesome rat food, which I and many breeders feed their rats. CLICK HERE FOR SUEBEE'S MIX

This is where my 4 ratties are housed: