Anxiety disorders in youths are globally prevalent and carry impairing, long-lasting effects. Interpreting ambiguous cues negatively may be causally related to adolescent anxiety. Extending cognitive bias modification of interpretations (CBM-I) training, which counters anxiety by encouraging positive interpretations, to anxious adolescents could inform the design of new interventions. The study investigates whether single-session CBM-I training (a) altered interpretation biases and negative mood in adolescents selected for high anxiety and (b) whether these training-associated changes were larger than those reported in low-anxious adolescents. Seventy-seven Chinese adolescents received either positive or control training. Positive training encouraged endorsement of positive interpretations of ambiguous scenarios while on control training trials, half of the scenarios were resolved positively and half negatively. A single session of CBM-I altered interpretation biases across all individuals, F(1, 52) = 10.63, p < .01, η2 = .17. However, no training effects on mood measures emerged (all ps > .05). Training effects were not consistently moderated by baseline trait anxiety. Multisession CBM-I may be needed for mood changes to occur.