A computer-aided system was devised to investigate the speaking space. Thirty native Cantonese speakers with Class I occlusion were selected and test sentences were designed for speech analysis by a Sona-Graph. The investigation indicated that the sibilant sounds produced the closest speaking space and that the mean and the variability of the closest speaking space in Cantonese speakers were smaller than that in English speakers. The beliefs that the closest speaking space was smaller than that of the freeway space and that the speaking space of m sound was similar to the freeway space were not supported by this study.