Corrosive behaviour of RME (rapeseed methyl ester) in blends with ultra-low sulphur diesel and GTL (gas-to-liquid) fuel is investigated in this study. The tests were carried out at a wide range of blending ratios and for two of the typical metals in manufacturing of engine parts in contact with fuel (aluminium and copper). Tests were divided into two main groups: short-term at elevated temperature (80 °C, 600 h) and long-term (room temperature, 5760 h). Effects of impurities such as presence or absence of dissolved oxygen and absorbed water were also investigated using the same test conditions. Before and after the tests metals and fuels have been investigated in many ways in order to understand the type and extend of the damage on both metal surfaces and fuel properties. Investigation of damages inflicted by fuel on metals was performed using scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS). Also nature of the oxide layer formed on the surface of the metal was studied using X-ray diffraction (XRD). Degradation of fuels as a result of exposure to metals was investigated for changes in kinematic viscosity, Total Acid Number (TAN) and any compositional changes in the fuel structure using GC–MS. Results revealed that biodiesel increases the corrosiveness of fuels exposed to both metals with more effect on copper samples, also it was found that the presence of dissolved oxygen and absorbed water is a key factor for more corrosion damage to metals. TAN value, kinematic viscosity and changes in the fuel composition all confirmed the degradation of the fuels as a result of exposure to the metals. GTL was found to be the most resistant fuel to corrosion, probably due to its chemical composition.