都市社區的公共事務治理在於創造良好環境品質；居民、管委會與其委外的管理維護公司，都扮演著關鍵的角色，但從許多研究與案例的報導中發現，大多數的都市社區治理難以協調這三者之間的和諧關係，他們彼此的策略互動，常引起社區治理的交易成本。因此，本研究從新制度經濟學的交易成本觀點並結合博弈理論的囚犯困境模型，探討居民、管委會與管理維護公司等三方參與者，彼此交易關係的互動演化，及社區管理的交易納入組織將對社區治理的交易成本與困境帶來何種影響作一分析，並以台南縣市公寓大廈為案例，實證參與者的擇優策略對社區治理的影響。本研究發現，居民面對公共事務治理活動，選擇不願參與或不合作是普遍存在的擇優策略。基於降低交易成本，管委會的組織因而形成納入社區公共事務的治理活動。但在居民缺乏參與意願及不願監督下，管委會面對公共事務的治理，會伺機去競爭社區資源或無形地耗費社區資源，是普遍存在的擇優策略。基於進一步降低交易成本，社區治理的工作於是外包給管理維護公司。但管理維護公司將視居民與管委會之間的矛盾與衝突，以伺機迴避及推諉難度高的工作並偏好容易做的工作，是管理維護公司的擇優策略，同時也會善用資訊優勢，以增進自身企業的獲利。

The quality of the urban communal environment depends on the collaboration among homeowners association, residents, and property management companies. However, many references show that their relationship is not harmony. Therefore, the main purpose of this paper is to theoretically analyze these three actors’ institutional incentives and behaviors under current urban communal governance based on the transaction cost perspectives. Moreover, the paper also investigated 26 communities in Tainan County compared to the theoretical analysis. The results show that the rational choice of residents is to be free riders in communal governance, which is constrained by the prisoner dilemmas. Hence, the transaction cost is very high in communal governance through voluntary cooperation that the institution of homeowner association is emerged in urban communal governance. However, the board members of homeowners also lack incentives and professions to purse the benefits of the whole community but may narrowly focus on their personal or small groups’ interests, which also creates transaction cost. Therefore homeowners association contracted out most functions of urban communal governance to property management company. However, property management companies under this institutional structure of urban community in Taiwan will rationally choose to satisfy the demand of board members to sustain the contracts and ignore the demand of the majority residents. Furthermore, these property management companies also use their information advantage to do rent seeking behaviours, which also create transaction cost. How to reduce these transaction cost in current urban communal governance needs more future researches to address.