The objective of this invention is to provide a composition for changing the expression of a clock gene and for changing the circadian rhythm by the expression change. The result of intensive research clearly indicates that an aqueous extract of Silktree Albizia bark can change the expression level and the phase of the clock gene. In addition, through oral administration of the aqueous extract of Silktree Albizia bark, it was found on subject that the afternoon drowsiness is decreased, the lucidity, will, mood and concentration ability are increased, and early morning tendency becomes stronger.本發明之目的在於提供一種用於使時鐘基因之表現變化，且藉由該表現變化而使晝夜節律變化之組合物，經過努力研究，結果明確得知合歡樹皮之水萃取物能夠使時鐘基因之表現量及相位變化。又發現，藉由經口投予合歡樹皮之水萃取物，受驗者午後睡意減少，而且清醒度、意志、情緒及集中力提升，清晨型傾向增強。
