The chikungunya virus (CHIKV) is transmitted by female Aedes aegypti and Aedes albopictus mosquitoes, mostly present in (sub)tropical regions. No antivi-rals are available to treat CHIKV infections. If antiviral drugs are proven efficient to treat CHIKV-infected patients, it will be pivotal to determine whether drug-resistant viruses can be transmitted from one human to another by their mosquito vectors. We orally infected Aedes aegypti mosquitoes with a blood meal containing wild-type or drug-resistant CHIKV variants (i.e., MADTP res CHIKV, with mutation in the nsP1 gene, and T-705 res CHIKV, with mutation in the RNA-dependent RNA polymerase [RdRp] gene). Viral loads were quantified in bodies (infection), heads (dissemination), and saliva (transmission) of individual mosquitoes. The infection rate of the resistant viruses was similar to that of the wild-type virus. However, the dissemination of T-705 res CHIKV was markedly decreased compared to wild-type and MADTP res CHIKV. Furthermore, T-705 res CHIKV was only transmitted in the saliva at day 20 postinfec-tion (p.i.), whereas transmission of wild-type CHIKV was observed at day 3 p.i. The attenuated phenotype of the T-705 res virus was confirmed in mosquito cell culture, whereas the replication fitness in Vero cells was similar to that of the wild type. In bodies and heads of mosquitoes infected with the resistant variants, the resistant phenotype and genotype were retained. Also in the saliva, the resistant genotype of MADTP res CHIKV was maintained. Our results illustrate that the fitness of drug-resistant variants should be evaluated in both hosts to be able to select antiviral drugs with a limited risk for the spread of drug resistance by mosquitoes. IMPORTANCE Because of its global reemergence and unusual morbidities associated with infection, the chikungunya virus (CHIKV) has become a substantial public health problem. However, no antivirals are currently available to treat CHIKV infections. If antiviral drugs will prove to be efficient to treat CHIKV-infected patients, it will be essential to understand if drug-resistant viruses can be transmitted from one human to another by the mosquito. We therefore orally infected Aedes mosquitoes with drug-resistant CHIKV variants and determined the replication and transmission levels. One of the antiviral drug-resistant CHIKV variants could efficiently replicate and disseminate in both laboratory and field-collected mosquitoes. In addition, this variant retained its drug-resistant genotype in the saliva. In contrast, the other drug-resistant variant was markedly attenuated in mosquitoes. Our results illustrate that extra caution for drug resistance should be considered when developing an antiar-bovirus antiviral in order to minimize the risk of spreading drug resistance by mosquitoes .