Abstract: A system for diagnosing autism comprises a measuring device, a movie display, a speaker, and a computer connected with the measuring device and the speaker. The computer contains a control program therein, the control program being capable of arranging a sequence of human-voiced syllables in a pseudo-random order and allowing the sequence of the human-voiced syllables to be played from the speaker while a silent subtitled movie being played on the movie display. The measuring device can measure brain response of a patient to obtain an averaged MMN value, which can be compared with a cut-off point by the control program, whereby, if the averaged MMN value is less than the cut-off point, the patient is deemed to have suffered from an autism. The present invention can provide objective data for quantitative analysis for autism, and provide an easy way to diagnose autism.