Yes, 1/3 is a rational number. A rational number is any number that can be expressed as the quotient or fraction p/q of two integers, where p is the numerator and q is the non-zero denominator. In the case of 1/3, the numerator is 1 and the denominator is 3, both of which are integers. Since the denominator is not zero, 1/3 fits the definition of a rational number.
Rational numbers include all integers, fractions, and repeating or terminating decimals. Since 1/3 can be expressed as a fraction of two integers, it is indeed a rational number.