製程能力指標是用一個指標的數值來衡量製程是否具有製程能力，大部份有關製 程能力的研究均著重於產品的規格區間為對稱的情況，當產品規格區間為非對稱的情況時， 是一般研究者較為忽略的。Boyles[2]回顧一些現有的指標同時提出六個處理非對稱規格區間 的指標。很不幸地，這些指標並不能完全的測出實際的製程能力。因此，吾人提出一個適用 於非對稱規格區間的新製程能力指標，再根據Choi及Owen[4]對製程能力指標的觀點與比 較方法來比較新指標與其他現有的指標，比較結果顯示新指標能更準確的測出實際的製程能 力。

　　　　　Process capability indices(PCIs), whose purpose is to provide a numerical measure on whether a production process is capable of producing items that satisfy the quality requirement preset by the customers, have received substantial research attention. Most research work, however, have focused on developing and investigating PCIs for processes with symmetric tolerances. PCIs for populations with asymmetric tolerances have been comparatively neglected. Recently, Boyles[2] reviewed several existing PCIs and proposed four new indices to handle populations with asymmetric tolerances. Unfortunately, those indices do not reflect process capability accurate enough. In this paper, we propose a new capability index so that positive uses of PCIs can be continued. The proposed new index is compared with the existing PCIs in terms of a process characteristic discussed in Choi and Owen [4]. The results indicated that the new index reflect process capability more accurately than the existing ones.