The purpose of this study is to clarify the neck injury mechanism during low speed rear impact. Low speed rear impact tests on human volunteers were conducted using a mini-sled apparatus with a mass production car seat. Head/neck/torso behavior and cervical vertebral motion were analyzed and strains on the cervical facet joint were determined. The effect of differences on gender, seat back angle, sled acceleration and muscle condition to the head/neck/torso behavior and the cervical vertebral motion were also discussed. Moreover, the risk of neck injury in a mass production car seat environment was evaluated by comparing the strain values to the results from a previously reported test that used a rigid seat environment.