本文對佛教「意業為（最）重」此命題進行分析與探究。全文主要分五個部份：首先，對《阿含經》經文出處做分析，可知佛教「意業為重」之基本觀點和立場。其次，以《成實論》為例解析正反見解，指出佛教特重「意業」，在於強調「心為法本」，一切由心念為前提而有所謂的善惡業可言。第三，指出佛教之強調「意業」，在於意本身即是業（身口則不然），此可從意、思、行、業此四者的密切連結看出；然而，此不代表身口行為並不重要，相對的，身口在業的造作中，具有增上助長之作用，而擴大業的效應，並增進意念的深度、強度。第四，佛教之重「意業」，顯示出善惡對錯的判定標準，有其獨到的倫理學特色而可特別注意；同時其中可能之限制，文末也提出初步反思。最後在結語指出，佛教之強調「意業」，不只挑戰古印度傳統，對應於現今倫理學暨哲學探討，亦多有省思及對話空間，值得進一步抉發及深化，而有更多論述的開展。

This paper is an investigation of the claim in Buddhism that 'mental action (”manaskarman”) is the most reprehensible for the performance of evil action.' There are five parts to the analysis: Firstly, I analyze the chapter in the ”agama” sutra where the claim first appears, so as to illuminate the basic view substantiating the claim that 'mental karma is the most significant (of the three karmas)'. Secondly, I analyze arguments for and against this claim given in the ”Satyasiddhiśāstra”, pointing out that the emphasis on 'mental karma' is to stress the 'mind as the root of everything.' All dharmas have mind as their basic premise onto which follows the formation of good or bad karma. Thirdly, I point out that the emphasis on 'mental karma' stems from the view that, unlike actions of body and speech, mental processes are karmic processes in themselves. This is illustrated by the close connection between ”manas”, ”cetana”, ”saṃskāra”, and karma. This does not however imply that actions of body and speech are unimportant. On the contrary, body and speech facilitate the formation of karma, expanding its effects and reinforcing the depth and strength of the agent's intention. Fourthly, the emphasis on 'mental karma' functions as an important criterion for judgments of good/evil and right/wrong, which carries its own ethical implications worthy of consideration. Towards the end of this section, I offer a preliminary reflection on the possible limitations of the claim. Lastly, I suggest that the emphasis on 'mental karma' not only challenges the philosophical tradition of ancient India, but further allows for reflection and dialogue within the study of contemporary ethics and philosophy. As such, further research on this topic is both meaningful and worthy of pursuit.