Context: Limited dorsiflexion (DF) range of motion (ROM) is commonly observed in both the athletic and general populations and is a predisposing factor for lower extremity injury. Graston Technique® (GT) is a form of instrument-assisted soft tissue mobilization (IASTM), used commonly to increase ROM. Evidence of the long-term effects of GT on ROM is lacking, particularly comparing the full GT protocol versus IASTM alone. Objective: To evaluate the effectiveness of 6 sessions of the GT or IASTM compared with a control (CON) group for increasing closed-chain DF ROM. Design: Cohort design with randomization. Setting: Athletic training clinic. Patients or OtherParticipants: A total of 23 physically active participants (37 limbs) with <34° of DF. Participants’ limbs were randomly allocated to the GT, IASTM, or CON group. Intervention: Participants’ closed-chain DF ROM (standing and kneeling) were assessed at baseline and 24–48 hours following their sixth treatment. Participants in the CON group were measured at baseline and 3 weeks later. The intervention groups received 6 treatments during a 3-week period, whereas the CON group received no treatment. The GT group received a warm-up, instrument application, stretching, and strengthening of the triceps surae. The IASTM group received a warm-up and instrument application. Main Outcome Measures: Closed-chain DF was assessed with a digital inclinometer in standing and kneeling. Results: A significant difference between groups was found in the standing position (P = .03) but not in kneeling (P = .15). Post hoc testing showed significant improvements in DF in standing following the GT compared with the control (P = .02). Conclusions: The GT significantly increases ankle DF following 6 treatments in participants with DF ROM deficits; however, no differences were found between GT and IASTM. The GT may be an effective intervention for clinicians to consider when treating patients with DF deficits.