Check your local bookstore for Barbie doll pricing guides. The condition of your doll is a major factor on whether or not it is valuable. Owning a doll in excellent-to-mint condition with original clothing (shoes too), and with its orginal box is most desirable to collectors.
It depends on the condition. Collectors pay more for mint condition- the more beat up the toy, the less they will pay. Also, it depends on what year it was. If it was quite a while ago and they stopped making it, then it would be worth more than usual.
When selling a collectible, it is important to realize that it must be in great to pristine shape. A Barbie is worth more in its box along with the original clothing and well kempt hair. Sometimes the oldest Barbie will not sell as well when "she" is missing these qualities.
This depends on the age, condition, and quality of the barbie doll. The most valuable dolls are those from before 1960, are in mint condition, and have the original clothes. They are worth more if still in the box.