本文建立一個雙占的垂直差異化模型，分別在價格競爭與數量競爭的架構下，分析企業社會責任對於均衡結果的影響，並進一步深入探究影響廠商投入CSR程度的因素。結果顯示，在價格競爭的情形下，廠商的產品訂價、利潤及CSR投入程度較低，相對地在數量競爭時，則是產品產量、消費者剩餘與社會福利較低。當廠商投入CSR的程度提高，無論在價格或數量競爭下，自身產品價格及產量都會提高，對手廠商的價格與產量則都降低，而市場上總消費者剩餘必然增加。最後，會影響到廠商採取CSR的是兩廠產品的差異化程度，在數量競爭時，投入CSR程度可能會因產品同質性高低而隨之有增減，價格競爭時則一定隨之提高而減少。;This paper investigates the impact of corporate social responsibility (CSR) on equilibrium solutions, and examines firms’ incentives for CSR investment under quantity and price competition respectively in a differentiated duopoly. Results indicate that compared to the equilibrium outcome under price competition, firms set higher prices, produce fewer outputs, obtain higher profits and adopt more CSR. Also, it is shown that consumer surplus and social welfare are larger under price competition. Furthermore, if a firm undertakes a greater level of CSR, both its price and output increase while them of its rival decrease, and meanwhile consumer surplus is enhanced. Finally, it is the degree of product differentiation that influences firms to undertake CSR activities. Under quantity competition, firms’ investments in CSR increase (decrease) in the degree of product differentiation when it is sufficiently low (high). Relatively, firms’ investments in CSR decrease in the degree of product differentiation under price competition.