By introducing the excess burden of taxation into unionized mixed and privatized oligopolies, we show that (i) regardless of the number of private firm, privatization of public firm is always desirable when the degree of the excess burden of taxation is small and (ii) when the degree of the excess burden of taxation is large, whether privatization or nationalization is desirable depends on the critical value of the excess burden of taxation. In contrast to the existing works on mixed oligopolies, we find that privatization can enhance social welfare regardless of the number of firms under mild conditions. Thus, the excess burden of taxation is relatively low for industrial countries since privatization is considered a powerful instrument for reducing distortionary taxation for policy reasons.