During the dengue epidemic in Yunnan Province, China, during 2019, a concurrent outbreak of chikungunya occurred in the city of Ruili, which is located in the southwest of the province, adjacent to Myanmar. As part of this outbreak, three neonatal cases of infection with indigenous chikungunya virus from mother-to-child (vertical) transmission were observed. Isolates of chikungunya virus were obtained from 37 serum samples of patients with chikungunya during this outbreak, and a phylogenetic analysis of these isolates revealed that they belong to the Indian Ocean subclade of the East/Central/South African genotype. The E1 genes of these viruses did not harbor the A226V mutation.