In the human population, spousal pairs have been found to share phenotypes, which demonstrates the highly nonrandom nature of human mate choice. However, assortative mating on blood type—one of the most fundamental phenotypes in biological, medical, and psychological studies—has not been investigated. Using a unique dataset from China, we provide statistical analysis to test whether matching on blood type is nonrandom and find a set of strong evidence for assortative mating on blood type. The findings are robust after we control for the effect of other possible mechanisms, and show that the spousal concordance on blood type we observe is attributable to not only an individual’s mate opportunity but also their mate choice.