The nonlinear Landau damping and growth of electrostatic waves in an electron beam-plasma system in a magnetic field have been observed experimentally. The space charge wave of the beam decays nonlinearly into the Trivelpiece-Gould mode, satisfying the resonant condition ω 0 -ω 1 -( k //0 - k //1 )ν b = m ω c ( m is an integer). This decayed wave can be amplified exponentially by increasing the amplitude of the pump wave. Similarly, an externally launched small amplitude test wave, having the same frequency as the decayed wave, can be amplified at the comparable rate. The nonlinear Landau damping coupling coefficients measured experimentally are in good agreement with theory. The virtual wave has also been observed. The pump wave amplitude decays strongly by the presence of the large amplitude test wave.