The quality of ignition and combustion of blends of soy biodiesel and marine fuels was evaluated. Faced with the increasing implementation of processes for converting heavier oil fractions, the availability of streams to formulate marine fuels has been reduced. In this context, the use of biodiesel is important to minimize problems caused by the retraction in production of these streams and improve marine fuel quality. Since composition and stability properties are of great importance and influence directly the combustion quality, the composition was determined using the SARA analysis by thin layer chromatography and a flame ionization detector and the mixtures' stability evaluation was made by optical scanning. Using the equipment Fuel Combustion Analyzer, mixtures of marine fuels and soy biodiesel were tested, varying the biodiesel content by volume in the mixture at levels up to 10% v/v. The results show that the addition of biofuel to marine fuels, in the evaluated conditions, does not compromise the combustion quality of the bunker oil and, in some cases, had even increased the estimated cetane number, indicating increased quality of ignition and combustion. (C) 2014 Elsevier B.V. All rights reserved.