本文從常祀、因祭的類型角度，探討東周祭祀祖先的齋戒日程，嘗試分梳歷代對《儀禮》士、大夫齋戒日程的爭議，並對照戰國楚簡的齋戒日數及其可能具有的意義。文中依序討論天子、諸侯、士、大夫宗廟常祀的齋戒進程與日數，得出從天子至士的宗廟常祀通行十日齋戒。繼而基於前賢的研究成果，觀察傳世文獻中因祭祖先的齋戒情形，並在此背景下，說明戰國楚簡中的禱祠齋戒日數不等，乃因祭性質使然，與傳世文獻相應。最後討論常祀、禱祠祖先齋戒日程的異同與可能具有的意義。禱祠在卜筮日、齋戒、祭祀的先後順序，與筮日禮之次日進行齋戒等，同於常祀。卜筮日禮與祭日的天干不同、齋戒未足十日則異於常祀。上述研究將有助於釐清齋戒日程爭議與戰國楚簡禱祠齋戒的定位。

This article aims to examine Zhai-Jie process in Eastern Zhou Dynasty in terms of two types of ancestor worships: the regular and the irregular. I will discuss first the differences of processes for the emperor, duke, Daifu, Shi in regular ancestor worship, and then examples of irregular ancestor worship. In regular ancestor worship, the Zhai-Jie will last exactly ten days; while in irregular ancestor worship, it usually last less than ten days. Because there are two types of worship, the days of Zhai-Jie are varied in historical documents, and this phenomenon can also be found in the dǎo (禱) in bamboo strips of Chu state. Finally, I will compare the differences of Zhai-Jie between the regular worship and the irregular worship in the hope of clarifying the understanding of Zhai-Jie in Eastern Zhou Dynasty.