The purpose of this study was to investigate the difference in the occlusal force between deviated and non-deviated sides of the mandible in adult patients with skeletal mandibular asymmetry, and then also compare the findings to those obtained from controls. The absolute and balance data of the occlusal pressure, occlusal contact area and occlusal force of 23 patients and the controls were examined. Correlations between the occlusal force and the morphology of the jaw-closing muscles were also analysed. The occlusal pressure of patients was not smaller than controls, however, the occlusal contact area and occlusal force in patients were significantly lower than those in the controls. There was no significant difference in the balance of the occlusal contact area and the occlusal force between the right and left sides in the controls, while the balance was shifted to the deviated side in the patients. Interestingly, the balance of the occlusal pressure was very similar between the patients and the controls. Most parameters of the morphology of the jaw-closing muscles did not show a linear correlation with either the occlusal pressure or force. In conclusion, the occlusal contact area and occlusal force in patients were significantly lower than those in the controls, and also the balance was shifted to the deviated side in patients with skeletal mandibular asymmetry. It is assumed that the morphology and orientation of jaw-closing muscles may have not linear but complex correlation to the weaker and unbalanced occlusal force in patients.