What is Buddhist ethics? This is an important and yet controversial question for contemporary Buddhism. This essay is to explore one undiscussed issue: the problems of Buddhist ethics constructed on "pratītya-samutpāda". For some Buddhist scholars such as Chao-Hui Shih, Ming-Fang Lee, Tetsuro Watsuji, Joanna Rogers Macy (maybe Wei-Hung Yen and Jay Garfield) do offer such an argument or theory for Buddhist ethics. The only merit of constructing Buddhist ethics on "pratītya-samutpāda" seems to unify Hīnayāna and Mahāyāna Buddhism. That is, since Hīnayāna and Mahāyāna Buddhists no doubt agree that "pratītya-samutpāda" is one of the Buddha's essential teachings, both should accept this construction of Buddhist ethics based on pratītya-samutpāda. However, whether it is appropriate is questionable (especially whether the idappaccayata of "pratītya-samutpāda" has the feature of interdependence or dependent co-arising) and this is the primary goal of this project. This paper principally will focus on Chao-Hui Shih's two books since they have more theoretical reasoning. We will explore the problems of Buddhist ethics constructed on "pratītya-samutpāda" from two aspects: from Shih's theory and from Buddhist ethics.