The purpose of this study is to find out the difference in circadian rhythm and level of fatigue between ER and General Ward Nurse. This study was done through analyzing body temperature, heart rate and major electrolytes such as Na+ and K+ concentration on urinalysis, which are related to factors of circadian rhythm and level of fatigue. The subjects, 17 nurses from Emergency Room and 25 nurses from general ward, were selected from a General Hospital in Taegu City on August 8 to 23, 1998. And the data were analyzed by proportion, t-test, chi-square and Pearson's Correlation, ANCOVA, using SAS program. The results of this study were shown as follows : First, The difference of Maximal and minimal heart rate was significant between ER group and general ward group. However, body temperature difference wasn't notable. Second, Urine Na+ concentration on urinalysis was lower and K+ concentration on urinalysis was higher in ER group than general ward group significantly. Third, Fatigue level was higher in ER group than general ward group significantly. Fourth, through urine concentration, significant relations in circadian rhythm of ER nurse group and general ward group and their fatigue level were found. Urine Na+ concentration on urinalysis of ER nurse was significant related with their fatigue level. In conclusion, the effect of fatigue on circadian rhythm is greater in ER group than general ward group during night shift. This study could be a help in improvement of nurse' s health and understanding the effect of fatigue on health.