既存探討民營化中立性定理（privatization neutrality theorem）的文獻忽略了近年來相當受到企業重視的環境企業社會責任（environmental corporate social responsibility, ECSR）。有鑒於此，本文建構一個公、民營企業皆進行 ECSR 活動的混合寡占模型重新探討民營化中立性定理。依據我們的研究結果顯示：（1）民營化中立性定理是否成立取決於生產活動是否具有外部性。當生產不具外部性時，民營化中立性定理成立，反之，則不成立。（2）當污染的邊際損害很大且ECSR 效果並不顯著時，政府的最適政策將為課稅而非補貼。（3）當生產具外部性時，即使考慮 ECSR 活動，民營化對社會福祉而言仍是不利的。

The existing literature on the privatization neutrality theorem ignores strategic environmental corporate social responsibility (ECSR), which has received considerable attention recently. To fill this gap, this paper constructs a mixed duopolistic model to re-examine the privatization neutrality theorem, in which both public and private enterprises can strategically carry out ECSR activities to increase consumers' willingness to pay for their products. The results of our research indicate that: (i) Whether or not the privatization neutrality theorem holds is contingent upon the externality of the production activities. When the production activities have no externality, the privatization neutrality theorem will still hold, otherwise, it will not. (ii) When the production activities have externality, privatization still has a negative impact on overall social welfare. (iii) When the marginal damage of pollution is huge and the ECSR effect is not significant, the optimal policy will be taxation rather than subsidy.

混合寡占; 民營化; 民營化中立性定理; 環境企業社會責任

mixed oligopoly; privatization; privatization neutrality theorem; strategy environmental corporate social responsibility