Abstract: This study used 'Youyu 26' buckwheat cultivar to analyze the effects of exogenous selenium (Se) on agronomic and physiological characteristics of buckwheat seedlings in plumbum (Pb) polluted soil in a pot experiment. The study determined the effects of exogenous Se on Pb content, and growth, development and output of buckwheat under soil Pb stress. The results of the study could lay the theory base for research on the use of Se to alleviate the toxicity of heavy metal Pb in plants. This was critical for developing the methodology needed for producing buckwheat and decreasing heavy mental contamination in agricultural fields. The experiment was set up in a two-factor complete random design, with five concentrations of Se (0 mg·kg^-1, 1 mg·kg^-1, 2.5 mg·kg^-1, 5 mg·kg^-1 and 10 mg·kg^-1) and three concentrations of Pb (0 mg·L^-1, 500 mg·L^-1 and 1 000 mg·L^-1). The results showed that with increasing concentration of Pb, plant height, total root length, dry weight, total root area, root activity, chlorophyll content, chlorophyll fluorescence parameters and economic yield (1000-grain weight, per-plant grain, etc.) of buckwheat decreased. Low Se concentration (1?2.5 mg·L^-1) alleviated Pb toxicity in buckwheat. The synergistic effect of high concentration of Se (5-10 mg·L^-1) increased Pb toxicity in buckwheat. Buckwheat total root length, root area, root activity and photosynthetic characteristics were highest and SOD and POD activities lowest at Se concentration of 2.5 mg·L^-1. Economic yield of buckwheat was highest when Pb tolerance of all organs of mature buckwheat was lowest at Se concentration of 2.5 mg·L^-1. Under the same Pb concentration, the Pb content in organs of buckwheat was decreased first and then increased with increased Se concentration. The Pb contents in different organs of buckwheat followed the order of root > stem > leaf > seeds under each treatment. Thus exogenous Se could be used to enhance buckwheat tolerance to Pb stress by inhabiting buckwheat absorption and transportation of Pb, promoting leaf photosynthesis and chlorophyll content along with root activity of seedling buckwheat. The research showed that suitable amount of Se (a recommended concentration of 2.5 mg·L^-1) could alleviate heavy metal toxicity in buckwheat.