ASEAN (Association of South-East Asian Nations) member countries are predicted to become a net importer of oil in the next 15-20 years. Therefore it is important to predict the future electricity demand in the region. However, predicting future electricity demand entail various issues and, one of them is its uncertainty. This study serves to reduce the uncertainties of predicting future electricity demand in the least and developing countries under ASEAN. Introducing the time-series relationship between economic and energy as an input in key parameters and GDP parameters on causality runs from economic to electricity and bi-directional economic and electricity. The result is then applied to predict the future electricity demand trend and is used as reference scenario. Policy, household size, power generation cost, etc are used as key assumption. Granger-causality test proves to be useful in order to predict the future electricity demand trend in Cambodia with the errors during 2005-2008 periods merely 5-7% compares to the actual data. While in Indonesia the error for 2000-2008 predictions compare to the actual demand which is accounted 8% in average. © Springer 2011.