Post-event rumination (PER) has been seen as a key element in the persistence of social anxiety (disorder). Studies on PER-targeted intervention, e.g., cognitive restructuring (CR), has, however, received little attention in adults, not yet in youth. In addition, previous research showed that, compared to interaction, participants reported higher levels of PER after speech task. The main aim of the present study was to investigate the effect of CR targeting PER among socially anxious (Chinese) adolescents and also to compare the intervention effect between speech and interaction situations. The present study recruited a sample of 73 high socially anxious adolescents aged 12–16 years and then randomly assigned them into speech (n = 37) or interaction (n = 36) group, without control group. PER and social anxiety (SA) were measured before and after CR. Analysis of Covariance (ANCOVA) results showed that adolescents’ PER and SA symptoms were significantly improved with intervention with moderate to high effect size. Furthermore, the decrease in PER could significantly predict the improvement of SA. However, the intervention effect showed no difference between groups. Although no control group was included, one-session CR still showed its potential to improve participants’ PER and SA. Limitations and future directions were discussed.