Thoracic hyperkyphosis structurally alters the position of the scapula to cause forward shoulder posture. However, the effect of improved thoracic hyperkyphosis on forward shoulder posture is unclear. The objective of this study was to determine the effect of eight weeks of thoracic mobilization on improving thoracic hyperkyphosis and forward shoulder posture and determine the cutoff change ratio in kyphosis for improving forward shoulder posture using the decision tree method.