Forty two healthy guinea pigs were divided into two groups:experimental and control. An experimental model of cerebral concussion was established by pendulum impactor striking to the heads of guinea pigs in a free state. Cerebral concussion ensued in 26 out of 37 guinea pigs, which were in turn killed 3、6、12、24、48、72 hours and 1、2、3~4weeks after the strike. Extensive and obvious changes were found in the brain tissues of 26 guinea pigs with cerebral concussion. In addition to the nerve cells, nerve fibers were affected as well. Typical retraction balls of axons were seen 72 hours after the strike and lasted for 4 weeks. Reaction gliosis appeared a week later. No changes were discovered in the control group. Changes in brain tissues after concussion are also discussed in this article, especially the morphogenesis of retraction balls.