Pulse self-compression in air is experimentally demonstrated by use of 1kHz femtosecond laser pulses with input power on the order of GW. Under the conditions of different initial chirps, the temporal and spectral characteristics of the output pulse after being focused in air are studied in detail as a function of i nput pulse energy. The experimental results show that, the temporal duration of high-intensity femtosecond laser pulses could be shortened solely through nonlinear propagation in air, without any additional dispersion compensation. Moreover, with the input pulse negatively chirped, we observed that the spectrum and pulse duration could be compressed simultaneously, and near sech2 trans form-limited output pulses shorter than original laser pulse source were obtained.