<p>Most quasi-zero-stiffness vibration isolators (QZS-VIs) are highly sensitive to load deviation. When the load deviates from the rated mass, the isolation performance of QZS-VIs deteriorates in the isolation region, and significant changes occur in the static deflection. To address the problem of traditional QZS-VIs not adapting to variable loads, a double-quasi-zero-stiffness vibration isolator (DQZS-VI) with two zero stiffness points is proposed. First, the force and stiffness characteristics are derived, and the double-quasi-zero-stiffness (DQZS) condition is given. Then, the steady-state solutions of the DQZS-VI system are obtained using the incremental harmonic balance method. The effects of critical parameters, such as the stiffness ratio and mass ratio, on the frequency response and force transmissibility are thoroughly analyzed. Finally, the performance of the DQZS-VI system is compared with that of QZS-VI systems. The results demonstrate that the proposed DQZS-VI system can exhibit a very low initial isolation frequency under the rated load, indicating its suitability for low-frequency isolation. When a small load deviation occurs, the isolation performance of the DQZS-VI system can be enhanced. It can achieve a smaller static equilibrium point offset and lower transmissibility in the isolation region than QZS-VI systems under certain load deviations. Thus, the DQZS-VI shows great potential for applications involving load deviations.</p>