This study is devoted to the experimental validation of a theoretical model of large amplitude vibrations of thin spherical shells described in Thomas et al.[1]. A specific mode coupling due to a 1:1:2 internal resonance between an axisymmetric mode and two companion asymmetric modes is especially addressed. The structure is forced with a sinusoidal signal of frequency close to the natural frequency of the axisymmetric mode. The experimental setup, which allows precise measurements of the vibration amplitudes of the three involved modes, is presented. Experimental resonance curves showing the amplitude of the modes as functions of the driving frequency are compared to the theoretical ones. A good qualitative agreement is obtained with the predictions given in the model. The quantitative discrepancies are discussed and an improvement of the model is proposed.