[Objectives]  To investigate the relationship between the damage caused by Rhinoncus sibiricus, the amounts of certain biochemical substances in the leaves of different buckwheat varieties and defensive enzyme activity, in order to provide information for selecting pest-resistant varieties of buckwheat. [Methods]  The damage caused by R. sibiricus to buckwheat was investigate using the five-point sampling method in the field. The relative preference of R. sibiricus for four different buckwheat varieties (Meng 0208, Meng 0207, Jinku 6, Jinku 2) was determined in laboratory experiments. The amounts of major nutrients and secondary metabolites, and defense enzyme and protease inhibitor activity, in the leaves of different buckwheat varieties, were also determined. [Results]  Stem-damage rates on the Meng0208 and Jinku2 buckwheat varieties were 59.22% and 65.23%, respectively; higher than on Meng0207 and Jinku6, which were 47.21% and 49.61%, respectively. The relative preference of R. sibiricus for different buckwheat varieties was: Jinku2>Meng0208>Jinku6>Meng0207. The amounts of soluble protein, soluble sugar, proline, flavonoids and total phenol in insect-resistant buckwheat varieties were significantly lower than in insect-sensitive varieties (P<0.05). There was a significant, positive correlation between the relative preference of R. sibiricus for different buckwheat varieties and the amount of soluble protein (R=0.840), soluble sugar (R=0.883), proline (R=0.750), flavonoids (R=0.809) and total phenol (R=0.729) in leaves. The activities of phenylalanine aminolase, catalase, trypsin inhibitor and chymotrypsin inhibitor were significantly higher in insect-resistant buckwheat varieties than in insect-sensitive varieties (P<0.05). There was a significant, negative correlation between the feeding preferences of R. sibiricus for different buckwheat varieties and the activities of phenylalanine aminolase (R=﹣0.837), catalase (R=﹣0.548), trypsin inhibitor (R=﹣0.579) and pancreatic protease inhibitor (R=﹣0.797) in buckwheat leaves. [Conclusion]  R. sibiricus significantly preferred feeding on the leaves of Meng0208 and JinKu2, whereas Meng0207 and Jinku6 had the highest insect resistance respectively among the four buckwheat varieties tested. The palatability of different buckwheat varieties to R. sibiricus was closely related to their nutrient content, secondary metabolic substances, defense enzyme activity and protease inhibitor activity.