Chapter 5 - Number Theory and the Real Number System - 5.5 Real Numbers and Their Properties; Clock Addition - Exercise Set 5.5 - Page 308: 8

-3 is a rational number that is not a natural number.

Natural numbers do not contain negatives. Rational numbers can be written $\frac{p}{q}$ where q $\ne$0. Since -3 can be written as $\frac{-3}{1}$, it is considered a rational number.