Methodology and application of Strategic Environmental Assessment (SEA) for policies, plans, and programs are still new approach in Vietnam. With a support from Vietnam-Swedish Project (SEMLA) and Ministry of Natural Resources and Environment (MONRE), SEA for the Tonkin Gulf Coastal Economic Belt Development Plan was conducted in 2008. Lessons obtained from this SEA may contribute to improving methods and practicing SEAs for regional development. The main lessons summarized in this paper are: (i) close cooperation between the planning and environmental teams from the beginning phase of a master plan; (ii) SEA should focus not only on impacts to the natural environment but also on main issues of socio-economic aspects; (iii) approaches and methods used in SEA should be appropriate to properly predict the impacts at regional-levels and cumulative impacts; (iv) a good SEA study may be achieved when detailed data on the environment and socio-economy of the study area are available and have active engagement of stakeholders, including project affected sectors, ecologists, planners, policy makers, etc. This paper is useful for whom, those work in SEA in regional development.