A spectral analysis is made of the observed P waves radiated by the Brazil earthquake of November 3, 1965, for the study of its source mechanism. The observed amplitude spectra have been equalized to the source by correcting for the instrument response, the crust response, and the mantle response. Radiation patterns are drawn as a function of azimuth around the focus and compared with theoretical radiation patterns for different source parameters for a best fit. The focal mechanism solution determined in this way corresponds to a double couple source model and is in good agreement with P-wave initial motion and S-wave polarization data. The presence of the effect of the finiteness of the source on the spectra of P waves is also noted.