The purpose of this study was to investigate the effects of yeast polysaccharide (YPS) on growth and flavonoid accumulation in sprout cultures of Fagopyrum tataricum (tartary buckwheat). Without obvious change in the appearance of the sprouts, the exogenous YPS notably stimulated the production of functional metabolites in F. tataricum sprouts, and the stimulation effect was concentration-dependent. With 400 mg/L of YPS applied to the sprout cultures on day 6, the total rutin and quercentin content was effectively increased to 42.8 mg/gdw, or about 1.4-fold in comparison with the control of 31.2 mg/gdw. Feeding with 800 mg/L of YPS on day 9, the sprouts biomass was increased by about 8% compared to the control culture (0.99 gdw/100 sprouts versus 0.92 gdw/100 sprouts). Moreover, the present study revealed that the accumulation of these bioactive metabolites resulted from the stimulation of the phenylpropanoid pathway by YPS treatment. It could be an effective strategy for improving the functional quality of the F. tataricum sprouts provided with YPS.