The purpose of this study was to investigate the effect of morning-night differences and sleep deprivation on situation awareness and driving performance. Twelve male students (mean of age 21.0+/-0.7 years old) participated in this study. They drove in following driving scenarios under three conditions: night condition, morning condition with and without sleep deprivation, on a driving simulator. Statistical analysis on situation awareness (SA) data shows that morning-night differences and sleep deprived condition during driving significantly affect Level 1 SA (F-(2,F-22)=18.54, P<0.01), Level 2 SA (F-(2,F-22)=14.47, P<0.01), and Level 3 SA (F-(2,F-22)=4.54, P=0.03). There are also significantly higher risky driving behavior score when driving in the morning with sleep deprived condition, as compared to driving in the Morning with proper sleep (P<0.01). The results of this study suggested that sleep deprivation or driving at night produced a degradation of situation awareness and a higher risky driving behavior.