The prediction of the sea echo Doppler spectrum of VHF and HF radio waves is important for the ocean wave remote sensing by VHF and HF radars. The authors extended the theory of the sea echo Doppler spectrum. In previous theories it is assumed that the scale of the illuminated area is much larger than the dominant wavelength. However, the effect of the finite illuminated area may not be negligible. The authors considered the effect to predict second-order sea echo Doppler spectrum and extended previous theories. Furthermore, the authors developed the numerical technique to compute radar cross sections of the extended theory. As a result, the agreement between measured and predicted Doppler spectra is improved. ¿ 2001 American Geophysical Union