<p>Selective anion transport is essential for energy conversion, water purification, and electrochemical systems, yet achieving precise ion selectivity in membranes remains a challenge. Here, we present an amino-functionalized graphene oxide (am-GO) membrane that enables tunable anion transport through nanochannels. Using a combined experimental and computational approach, we consider the three stages of ionic transport—absorption, diffusion, and desorption—to reveal that Cl⁻ selectively diffuses through nanochannels, while NO₃⁻, SO₄²⁻, and PO₄³⁻ are excluded. In ionic mixtures, the chemical transistor effect emerges, where Cl⁻ pulls water from NO₃⁻ hydration shell, enhancing its mobility, while SO₄²⁻ and PO₄³⁻ remain excluded due to size constraints. This mechanism enables precisely regulated Cl⁻ and NO₃⁻ transport, with ultrahigh rejection rates of 99.99% for SO₄²⁻ and PO₄³⁻, even in complex ionic environments. The am-GO exhibits stability and anion-hopping mechanisms, making it a versatile platform for anion exchange membranes in electrolysis, energy storage, and environmental applications.</p>