A　driving　simulator　experiment　was　carried　out　to　validate　the　effect　of　the　environmental　sound　as　a　fatigue　countermeasure.　Various　types　of　the　simulating　sound　source　were　synthesized　by　different　intensities,　frequencies,　and　durations　of　sound.　The　monotonow　scene　at　midday　was　chosen　to　do　experiment　because　of　initiating　easily　the　fatigue　symplom.　The　eye　movement　and　the　other　facial　features　were　used　as　the　criteria　for　fatigue　judgment.　The　sound　stimuli　were　given　as　the　fatigue　symptom　appeared,　and　the　variations　of　the　driver　physiological　signals　including　the　electroencephalogram,　the　electwcardiogram,　and　the　eye　movement　and　his　driving　performance　were　analyzed　before　and　during　the　sound　stimulation.　The　results　showed　the　alerting　reaction　exists　for　the　monotonous　sound　stimulation　when　the　driver　is　in　the　fatigue　state,　but　the　alert　only　lasts　for　a　few　minutes.　The　type　of　the　stimulating　sound　affects　significantly　on　the　result　of　stimulation.　Therefore,　it　is　necessary　to　further　study　the　effects　of　various　factors　of　the　sound　against　the　driving　fatigue　and　establish　a　lasting,　alerting　sound　combination　as　an　effective　driving　fatigul　countermeasure.