We reported, to the best of our knowledge, the first experimental evidence of the pulsating soliton with chaotic behavior in an ultrafast fiber laser. By virtue of a dispersive Fourier transformation method, the chaotic behavior of soliton pulsation is visualized by the fact that the mode-locked spectrum collapses abruptly in an unpredictable way during the pulsating process. The obtained results provide the experimental demonstration of the chaotic behavior in the pulsating soliton, which would also give some new insights into the soliton pulsation dynamics in dissipative systems.