An experimental study has been implemented to elucidate a resonance of natural convection in a side-heated enclosure with a mechanically oscillating bottom wall. The impetus of the present study is to provide an experimental verification of the resonant frequency of natural convection that has been numerically predicted so far. The experimental results show that the amplitude of fluctuating air temperature inside the enclosure peaks at a particular frequency of the bottom wall oscillation, which is indicative of resonance. The resonant frequency increases with the increase of the system Rayleigh number and it is little affected by the increase of forcing amplitude. The resonant frequency measured in the present experiment is in good accordance with the previous numerical predictions in which the models are based on the degree of thermal stratification in the interior.