Introduction: The parameters of Achille tendon is critical in allograft anterior crudate ligament reconstruction. Objective: Determine the practical diameter of allograft Achille tendon. Material and method: 34 allograft Achille tendons were harvested. The practical diameter was measured by mathematic method. Results: The average of practical diameter of allograft Achille tendon is 10,32 + or - 0,48, there is significant difference between male and female. Conclusion: The practical diameter of allograft Achille tendon is big enough to reconstruct the anterior cruciate ligament arthroscopically.