Copepod Mesocyclops as biological control agents for dengue was previously proven to be effective and sustainable in the Northern and Central provinces of Vietnam. We aim to study social sustainability of Mesocyclops intervention in south Vietnam. Both quantitative and qualitative approaches were used. An entomological survey was carried out in 100 random households of Chanh An commune, Vinh Long Province. Aedes larval indices and Mesocyclops prevalence were compared with historical pre- and post-intervention values. In the same commune, using purposeful sampling, sixteen semi-structured interviews (1 villager leader, 1 local doctor, 10 villagers, 2 teachers, 2 entomology officials), and a focus group discussion (6 Mesocyclops program collaborators) explored water storage habits, beliefs about dengue prevention and behaviour related to Mesocyclops. Thematic analysis was conducted to interpret the qualitative findings. Aedes abundance increased after responsibility for Mesocyclops intervention moved from government to community in 2010, with post-transfer surges in Breteau Index, Container Index, and Larval Density Index. Larval increments coincided with decrease in Mesocyclops prevalence. Villagers had some knowledge of dengue but it was conflated with other mosquito borne diseases and understanding of Mesocyclops was incomplete. Program adoption among the villagers was limited. With reduced government support program collaborators reported limited capacity to conduct population monitoring, and instead targeted 'problem' households. Although the Mesocyclops program was highly sustainable in northern and central provinces of Vietnam, the intervention has not been consistently adopted by southern households in Chanh An commune. Limited education, household monitoring and government support are affecting sustainability. Findings were based on a small household sample visited over a short time period, so other evaluations are needed. However, our results suggest that government support for the Mesocyclops program is still required in this part of Vietnam.