Purpose <p>Botulinum toxin (BTX, Botox) is increasingly used as an adjunct therapy to oral steroids in the management of facial paralysis, with positive outcomes. This study aimed to evaluate the additive effect of BTX injection on the non-paralyzed side and propose optimal injection timing for recovery time.</p> Methods <p>A total of 48 atraumatic facial paralysis patients who visited Seoul St. Mary’s hospital for facial palsy between June 2015 and May 2021 were retrospectively reviewed. Patients were divided into 2 groups: the BTX injection group (BG) and the non-BTX injection group (NBG). We analyzed the recovery rate of facial palsy to H-B grade II or lower in each group, and conducted telephone surveys to collect subjective satisfaction data after BTX injection.</p> Results <p>Days of recovery to H-B grade II from symptom onset were 93.0 ± 62 and 68.7 ± 66.6 in NBG and BG, respectively. Early BTX injection (less than 17.5 days from symptom onset) was a prognostic factor for recovery to H-B grade II in less than 1 month (R² = 0.935, B = 1.738, <i>p</i> &lt; 0.001). Telephone survey showed subjective satisfaction in all aspects 1 month after BTX injection: function (83.3%), cosmetic (70.9%), and recovery (54.2%).</p> Conclusion <p>Early contralateral facial BTX injection can shorten the recovery period of atraumatic facial palsy.</p>