In this article, a novel and high-performance mesoporous carbon-based solid acid catalyst was prepared using ethylene tar (ET) as a precursor, which is a byproduct of ethylene production. First, ET was carbonized at 550 °C by using magnesium acetate as the template. After that, the mesoporous ET-based solid acid catalyst was obtained by a one-step sulfonation process that removes the templates simultaneously. On the basis of these facts, the maximum yield of 5-hydroxymethylfurfural (5-HMF) in the presence of an ET catalyst during the dehydration of fructose can reach 87.8%. This effective catalytic activity is mainly attributed to the large specific surface area and high density of sulfonic acid groups existing in the ET catalyst. Moreover, no distinct activity drop was observed during five recycling runs that confirmed good recyclability and thermal stability of the ET catalyst. This research provides a novel and promising method for the utilization of ET as a low-cost, recyclable, and high-performance catalyst.