Abstract: An automatic endmember extraction method based on the extended morphology and the orthogonal subspace projection was proposed to solve the problems, including identification of different endmembers with similar spectra and the endmembers extraction used by the spectral or spatial information only. Extended dilation and erosion operators were used to calculate the morphological eccentricity index (MEI), and the MEI was used to extract the endmember set. Spectral angle matching (SAM) was applied to distinguish different endmembers, and then the endmember was projected to its orthogonal subspace to eliminate the effect of endmembers that had been extracted. The airborne hyperspectral data was used to evaluate the performance of this method. The results illuminate that image endmembers are extracted automatically without any prior information and endmembers with similar spectra are distinguished effectively.