This question is often asked by people who want to keep a small pet, but don't like the idea of a rat-like tail.
Gerbils do indeed have tails, and long ones too. In the Mongolian gerbil the tail is covered with a thin layer of fur, while the fat-tailed gerbil has a thicker, bald tail.
So, Mongolian gerbils, with their long, furry tails, make a more appealing pet for anyone who dislikes the look of a mouse or rat tail.
Gerbils have long, multi-purpose tails
Gerbils use their tails for balance and for losing heat during the scorching daytime in their native habitats. The fat-tailed gerbil uses the tail for storing fat reserves too. Other species use their tails to warn family members of any danger - they move their tails up and down and beat them on the ground, producing a visual clue along with vibrations that send the others scurrying for cover.