The solubility of ethanol in diesel oil with biodiesel is a limiting factor for its use as fuel for compression ignition engines. The stability of blends of ethanol with concentration varying from 5% to 30% in diesel oil containing 7% of biodiesel (B7) was evaluated at temperatures from 16°C to 25°C. The blends were conditioned in graduated glass cylinders and kept at the test temperatures, being observed the blend phase separation percentage in specific time schedules. The results show the stability time of each blend, indicating the maximum storage and use periods for the ethanol concentration evaluated. The results demonstrate that fuel blends with ethanol concentrations up to 15% can safely be used as engine fuels, as far as the tested parameters are concerned.