Skin damage by either trauma or surgical intervention inevitably results in scar formation. Facial scars can be cosmetically disfiguring and may cause functional impairment and psychosocial withdrawal. Botulinum toxin type A (BoNTA) is known to prevent fibroblast proliferation and expression of transforming growth factor-β1. It also induces temporary muscle paralysis and decreases tension vectors. Fibroblasts induce scar contracture and hypertrophy by producing collagen fibers in wound healing processes. In theory, botulinum toxin can play a vital role in scar prevention by reducing contracture and relaxing the adjacent muscles. Several studies have suggested the possibility of injecting botulinum toxin into nearby musculature around the traumatic or incisional wounds. However, sound clinical evidence has been missing. The aim of this study is to investigate the subjective and objective evidence of the effect that botulinum toxin has on scar formation in human. This is a prospective, split-scar, double-blinded, randomized controlled study. From February 2012 to December 2015, patients who presented forehead lacerations were recruited from the emergency room. Forty-five patients with forehead laceration were enrolled in this study and randomized into 2 groups with or without injection of BoNTA. When the patients presented to the clinic to remove the stitches, BoNTA was injected to the BoNTA group with 24 patients and saline was injected to the control group with 21 patients. The BoNTA was injected on dermal layer with 5 units/cm within a 0.5 cm distance on BoNTA group. Placebo drug was prepared as a vial containing 0.9% saline which is similar to BoNTA. After that, follow-up was done in 1, 3, and 6 months. The scars were analyzed with the Patient and Observer Scar Assessment Scale, Stony Brook Scar Evaluation Scales, and Visual Analog Scale and analyzed with independent t test, along with clinical photographs, cutometer, and biopsies. There were 21 patients in the control group and 24 patients in the BoNTA group. There were no significant adverse events in all patients. In all scar scales, the scores changed into favorable direction in both groups and the changes were larger in BoNTA group compared with the control group. However, when the amount of changes of the scar scales was investigated, there were more favorable changes in BoNTA group, which was proved statistically in Stony Brook Scar Evaluation Scales (P = 0.047) and Visual Analogue Scale (P = 0.046). Even without statistical significance, there were more favorable changes in BoNTA group in Patient Scar Assessment Scale (P = 0.110) and Observer Scar Assessment Scale (P = 0.169). Skin biopsy showed less collagen deposition on dermal layer in BoNTA group. In hematoxylin and eosin stain and Masson-trichrome stain, there was a denser deposition of collagen fibers of the specimen belonging to the control group compared to the BoNTA group. Based on the findings above, BoNTA can improve scar properties in various aspects, especially in decreasing collagen synthesis. The gross findings also showed favorable changes. This study provides useful indication of application of BoNTA in scar prevention with promising results.