Yes, 2/3 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 this case, 2 and 3 are both integers, and 3 is not zero. Therefore, 2/3 fits the definition of a rational number.
Rational numbers include all integers, fractions, and terminating or repeating decimals. Since 2/3 is a fraction of two integers, it is clearly a rational number.