This study was analyzed about influence of the seat back strength on neck injury in low speed rear offset impacts. MADYMO human model with the detailed neck model was used to define the magnitude and direction of internal forces acting on the cervical spine during rear impact. The analysis of neck motion and soft tissue neck injury(STNI) were studied using the lumped parameter model. Increased strength of the seat back resulted in increased ligament and disc forces. On the other hand, decreased strength of the seat back resulted increased force. It is clear that an appropriate strength of seat back allows to minimize a neck injury.