There may be two methods defining the rational exponent $a^{frac{m}{n}}$ for any positive real number a. The one which is used in all korean highschool mathematics textbooks is to define it as $sqrt[n]{a^m}$, that is $(a^m)^{frac{1}{n}}$. The other is to define it as $(sqrt[n]a)^m}$, that is $(a^{frac{1}{n}})^m$. In this paper, we insist that the latter is more appropriate and universal, and that the contents of current textbooks on the definition of the rational exponent should be corrected.