In this work, we propose a novel bio-inspired swing decoupling mechanism supporting high precision motion systems, which is composed of multiple co-directional input branches with a rigid swing unit and an anti-rotational guiding unit. By actively adjusting the input displacements, the decoupling mechanism can switch between the swing and translational modes, where the parasitic rotations can be significantly suppressed by the anti-rotational guiding unit. With this, fully decoupled X and Y linear motions are obtained in the presence of co-directional input branches. A theoretical model of the decoupling mechanism is also established to accurately describe the decoupling behavior, which is verified by finite element simulations. A prototype of the proposed swing decoupling mechanism is fabricated and instrumented with comprehensive experimental apparatus, where the experimental results effectively validate the excellent decoupling performance and demonstrate good potentials to precision engineering applications.