Abstract: The index of sustainable functionality (ISF) was applied to assess the impact of the Marina Bay development project on the sustainability of Singapore. The development project has three aims: water supply, flood control and lifestyle attraction; construction for the various stages began in 2005, with scheduled completion end of 2009. The period of study was 2001–2007, before and during construction. The ISF increased from 2001 to 2004, then decreased slightly and stabilised from 2005 onwards, staying below the 2004 ISF value, showing that the development has not increased sustainability. A quick forecasting exercise, for the case that the three aims above were achieved and all other indicator values the same as those in 2007, increased the ISF value by 5.1%. Continued ISF construction would indicate if the functionality, and thus sustainability, of Singapore would increase after the Marina Bay development is completed and the benefits can be realised.