This study examined the daily rhythmic patterns of mood in shift workers. Ten rotating shift nurses (shift worker group) were matched with ten non-rotating student nurses (non-shift worker group) working under the same conditions at CUniversity Hospital. The subjecs completed the Mood Adjective Checkist(MAC) every two or three hours from 6AM to 9-11 PM for six consecutive days. The MAC was constructed by Mansour and coversed the mood factors of Anger-Depression. Happiness, Mental, and Social. These data were analyzed by using Cosinor method. The results are summarized as follows; 1. There was no difference in mean scores for Anger-Depression, Happiness, Mental, and Social mood rhythm between the shift workers and the non-shift workers. 2. There was no difference in the amplitude of Anger-Depression, Happiness and Social mood between the two groups, but the shift workers had a higher amplitude of Mental mood. 3. The acrophases of the Anger -Depression mood were between 1:28 and 2:05, and those of Happiness, Social, and Mental mood were between 12:5 and 15:03 for both groups. There were no diffirences between the groups. 4. The number of the subjects with statistically significant mean cosinor rhythms for Anger-Depression and Mental moods were higher in the shift workers than in the non shift workers, but there were no differences between the shift workers and the non-shift workers in those of Happiness and Mental mood. This study showed that the mood manifested circadian periodicities, and a rapidly rotating shift system did not changed the circadian rhythm of mood. It is expected that this study will facilitate a better understanding of circadian rhythm in mood in the shift workers.