A quasi-zero stiffness isolator is designed and presented by parallel connecting a linear isolator and the Euler buckled beams formed negative stiffness mechanism. The basic feature of the quasi-zero stiffness isolator is that it has high support capacity and zero dynamic stiffness at the equilibrium point after loaded. Higher order of approximation of the restoring force of the isolator using Taylor expansion is adopted which can improve the response results solved by Harmonic Balance Method (HBM). The performance of the zero stiffness isolator is compared with that of an equivalent linear one by defining the force transmissibility for both isolators. The results show that the quasi-zero stiffness isolator proposed is superior to the linear isolator over the isolation frequency range and the peak transmissibility. Furthermore, the performance of the quasi-zero stiffness isolator becomes better with the decrease of the excitation amplitude, making it ideal for use in small amplitude and even micro-vibration isolation applications.