Climate change, particularly salinity intrusion has been amplifying pressures and stresses on coastal agricultural production in the Mekong Delta of Vietnam. The transformation of farming systems, mainly shifting to mono-shrimp culture is considered as an unavoidable option in the coastal regions. However, the transformation is quite risky in terms of technical aspects, financial feasibility, and environmental management. Besides, shrimp production is one of the production activities that seriously affect the environment. Therefore, the study aims at estimating the environmental efficiency of transformed shrimp farming.  The study conducted interviews with 90 farmers who recently shifted from sugarcane cultivation to mono-shrimp culture in Cu Lao Dung district, Soc Trang province. The findings show that on average the annual benefit of mono-shrimp culture was 419 million VND ha^-1. However, the benefit varies greatly among farmers, indicating that the magnitude of risks of transformed mono-shrimp production is high. The study also shows that about 91% of farmers got loss at least one time since the transformation. We also found that the average output-oriented technical efficiency was about 72.74%, suggesting that the shrimp farmers could increase their output level by about 27.26% while keeping inputs constant. The environmental efficiency on the average was approximately 65.44%, indicating that the farmers could contract their environmentally detrimental inputs by 35%, given the current levels of normal inputs and output level.