Abstract: Shock wave propagation in relaxing fluid is studied theoretically and experimentally. Modified spectral method is used in numerical simulations to provide an accurate description of weak shocks. For the medium with only one relaxation time, the waveforms of initially triangular pulse with shock front are calculated at various distances. It is shown that nonlinearity results in additional increasing of pulse duration and additional suppression of shock front damping. Experiments are performed in acetic acid as a monorelaxing medium. Short pulses are excited by optoacoustic source. A relaxation time of the fluid is changed by temperature variation. It is shown that pulse distortion is sensitive to the temperature of the medium. A relaxation time is evaluated from the analysis of shock pulse waveform after passing a layer of acetic acid. Theoretical and experimental results are in a good agreement.