The development of radar technology has increased the possibility of warplanes being detected. Therefore, radar stealth capability is critical for warplanes. Currently, microwave-absorbing materials with plasticity are urgently needed to reduce the strong electromagnetic scattering from plenty of small gaps on aircraft. Here, we propose a strategy to encapsulate liquid metal with reduced graphene oxide (rGO) to form a plastic microwave-absorbing putty. The putty is formed by a self-assembly electrostatic method to create a sparse foam structure with good plasticity. Interestingly, the nonmagnetic putty not only shows a dielectric loss but also exhibits unique magnetic losses. This synergistic mechanism allows the putty to obtain a minimum reflection (RLmin) of −58.86 dB at 8.93 GHz with a small thickness of 3.57 mm. The excellent properties of this composite putty allow it to be a candidate for microwave-absorbing putties to reduce the radar cross section of airplanes.