The roles of fixed costs in models of imperfect competition have been extensively studied. Yet, the possibility that different types of fixed costs may lead to different implications is not systematically explored in the literature. This paper sets up a model of imperfect competition to examine whether different types of fixed costs-production-related or non-production-related fixed costs-influence the optimal tax rates. It is found that different types of fixed costs indeed play a crucial role leading to different implications concerning the optimal tax rates.