This paper proposes a new concept to enhance the efficiency of the vibration energy harvesting via an intermediate booster. The boosters have auxetic structures and exert extra stretching strain in two perpendicular directions. The concept is tested on a conventional cantilever beam under the base excitation. The problem consists of a cantilever beam subjected to a body load at low frequencies. An auxetic substrate is bonded to the beam with a thin epoxy layer, and the piezoelectric (PZT) element is attached on top of it. Two different auxetic structures are investigated in this study. It is shown that employing these kinds of boosters can remarkably enhance the performance of the energy harvesting system. The harvesting efficiency is numerically evaluated in different load amplitudes and frequencies. A parametric study is then carried out, and effects of different geometrical design parameters of the auxetic boosters on the performance of the energy harvesting system are investigated. Comparing with the case in which the PZT is straightly attached to the cantilever, it is shown that adding such intermediate boosters at low -frequency range can increase the extracted power by factors of 3.9 and 7.0 for the two proposed geometries.