The aim of this study was to create an economic decision-making tool to allow farmers and stakeholders to make informed decisions around costs, benefits, and risks involved in production of sandfish, Holothuria scahru. and Babylon snail, Babylonia areolata, in different coculture arrangements based on a sound economic framework. A small-scale (0.16 ha) farm operation in Vietnam was modelled using production data obtained in previous studies to represent the costs and returns of rearing sandfish in tank-based nursery systems and in pond-based coculture grow-out systems. Sandfish and Babylonia monoculture was compared with three coculture models where the two species were separated, and the amount of pond area allocated to each ranged from 25% to 75%. A fourth coculture model (Co-4; 'comingled') was assessed where the two species were not separated and shared 100% of the substrate. The sandfish monoculture system produced 487 kg of sandfish at an annual cost of USD 5,616. providing an annual return of USD -3.521. The largest annual cost associated with sandfish monoculture was labor (USD 8.04 per kg). Pond monoculture of Babylon snail returned USD 1.876 annually, with an annual production cost of USD 19,858. Feeding represented the largest production cost associated with Babylonia monoculture of USD 14,340 per annum, or USD 5.11 per kg. Sandfish monoculture and Babylonia monoculture returned benefit cost ratios of 0.37 and 1.09, respectively. The coculture model with pond area divided 50:50 between sandfish and Babylonia during grow-out, produced 258 kg of sandfish and 2,584 kg of Babylonia over a 359-day production cycle. This equates to USD 1,108 and USD 20,001 annual production of sandfish and Babylonia, respectively. After production costs, this model provided a return of USD 2.309 annually at a benefit cost ratio of 1.12. The comingled culture model. Co-4. provided the greatest annual return of USD 6,019 and a benefit-cost ratio of 1.24. Results of this study build on previous research into practical aspects of sandfish/Babylonia coculture and provide a more complete picture of the potential application of this research to improve livelihoods and income of small-scale farmers in Vietnam. KEY WORDS: Sea cucumber. Holothuria scabra, Babylon snail. Babylonia areolata. coculture, cost benefit analysis. Vietnam, INTRODUCTION Recent years have seen a rapid increase in marine and brackish water aquaculture production in Vietnam with a particularly rapid increase in pond-based culture of shrimp for which Vietnam [...]