This paper examines the impact of unilateral tariff increases on the world growth rate using a two-country endogenous growth model when firms are internationally mobile, technical knowledge in research and development is an international public good, and iceberg transport costs are not subject to tariffs. In this paper, we find that a unilateral tariff increase in one country raises or lowers the world growth rate, depending on the degree of elasticity of substitution between any two differentiated goods and the share of firms owned by the country that raised tariffs.