The authors try to discriminate foxtail millet and common millet by using δ¹³C values as indicator. The charred botanical samples studied were collected from archaeological sites，Qin′an  County and Li County，Gansu Province. They were identified as foxtail millet and common millet in terms of morphology. Using a Dleta Plus produced by Finigan，  δ¹³C  of each sample were analyzed of 12 couples of foxtail millet and common millet from Qin′an  and 14 couples from Li. As a whole，the δ¹³C  of charred foxtail millet trends more toward the positive than the  δ¹³C of charred common millet does. This trend may be used to test if the morphological distinguishing between foxtail millet and common millet is correct.