Biodiesel is a promising substitute fuel for fossil fuels that derived from renewable resources like vegetable oils and animal fats. Rapeseed methyl ester, RME, is the most common biodiesel used in Scandinavia. Chemically, biodiesel is unstable and degradation of biodiesel results in formation of corrosive degradation products such as short chain fatty acids (SCFA) and water.Degradation of biodiesel is a continuous process which takes place even during corrosion studies in laboratory and results in too aggressive fuel. In order to investigate how increasing acidity of degraded fuel influence corrosion of metals and to avoid too corrosive environment, a stable test fuel simulating degraded biodiesel with certain amount of corrosive degradation products but resistance to additional degradation was needed to be developed.In the first part of this project a stable test fuel has been prepared and doped by adding impurity (methanol) and corrosive degradation products such as SCFA and water to a saturated methyl ester in order to simulate the corrosive environment and avoid excessive aggressiveness during the corrosion testing .Then four batches of test fuel were blended to see how increasing acidity and water content will influence the metallic corrosion.In the second part, samples of copper, brass and aluminium, with focus on copper, were exposed to prepared test fuels and RME in order to investigate corrosion behaviour of the metals and their effect on the test fuels.In order to investigate the stability of test fuel and effect of metals on it, developed test fuels were evaluated regarding to its water content using Karl Fischer volumetric titration, SCFA using extraction ion chromatography, structure using GC-MS and methanol using GC-FID. Targeted acceptance criteria for developed test fuel; such as solubility of degradation products, oxidation stability, toxicity, melting point were fulfilled by test fuel.Corrosion rate of the copper samples was calculated and their surfaces were analysed with SEM-EDS and FTIR. Metal content of fuel samples were analysed after exposure using ICP-OES method.As expected copper accelerated the oxidation of biodiesel effectively and copper ions were released into RME or low acidic test fuel but with increasing the acidity in test fuel copper samples were corroded and the corrosion rate increased. The results showed that the developed test fuel enabled accelerated corrosion testing comparable with aged RME.