To convert the decimal 0.8 to a rational number, we can express it as a fraction.
Since 0.8 is the same as \( \frac{8}{10} \), we can simplify this fraction:
\[ \frac{8}{10} = \frac{4}{5} \]
Thus, the decimal 0.8 can be expressed as the rational number \( \frac{4}{5} \).