To investigate the effect of malocclusion on mandibular movement during speech, the Sirognathograph Analyzing System was used to analyze the form of the envelope of motion during speech, as well as the relationship between the envelope of motion and eccentric movement paths, in 10 normal subjects and 60 subjects having malocclusion. Location of the envelope of motion, and the relationship between the envelope of motion and eccentric movement paths, were closely related to specific malocclusions. It is suggested that analysis of the envelope of motion during speech has diagnostic value in speech function assessment and that its detailed analysis offers valuable information for diagnosis and initiation of dental treatment.