The fusion between synthetic vesicles is an interesting mechanism for the stepwise construction of vesicle compartments for origins of life models and synthetic biology. In this communication, we report an innovative study on the not well-known case of fusion between oppositely charged vesicles, in particular by using fatty acid vesicles and DDAB as cationic surfactant. By combining fluorescence, turbidity vs. time profiles and vesicle size distribution obtained by dynamic light scattering, we show that POPC/oleate 1/4 mol/mol anionic vesicles can be fused with POPC/DDAB 1/1 mol/mol cationic vesicles with about 20% yield. Other non-fusion processes also occur, vesicle fusion being more effective by reducing the ionic strength of the buffer. This study also contributes to clarify the term "vesicle fusion", which is not always properly used in describing reactivity among vesicles. (C) 2010 Elsevier Inc. All rights reserved.