An aluminum‐tolerant cell line was selected by exposing carrot cell suspension cultures to excess Al, and properties of the selected cells were investigated to elucidate the mechanism of Al‐tolerance. One marked physiological property of the selected cells was that they released more citric acid in the medium than the nonselected cells, particularly in the presence of Al. The Al‐tolerance of the selected cell line was related to the chelating effect of citric acid, which was released abundantly to the medium from the cells. The tops and roots of the germinates from the nonselected cells hardly elongated in the presence of 1 mM AlCl3, but those from the selected cells did very well. Results of visual examination on Al‐tolerance by hematoxylin staining of roots agreed with those obtained by the root elongation test.