Let \(\gcd (m,n)\) denote the greatest common divisor of the positive integers m and n, and let \(\mu \) be the Möbius function. For any real number \((x > 5)\) , define the summatory function involving the greatest common divisor by \( S_{\mu }(x) := \sum _{mn \le x} \mu (\gcd (m,n)). \) In this paper, we establish an asymptotic formula for \(S_{\mu }(x)\) . Under the assumption of the Riemann Hypothesis, we further refine this formula and derive a mean square estimate for the corresponding error term.