The present work investigates the effects of biodiesel contamination on conventional and renewable marine diesels, i.e., NATO F-76 and HRD-76. The physical properties and chemical composition of F-76, HRD-76, and biodiesel were measured, including viscosity, density, peroxide value, heat of combustion, and acid number. Long-term (ASTM D4625) and accelerated (ASTM D5304) test methods were used to investigate the influence of biodiesel contamination on storage stability of HRD-76, F-76, and their blends. The impact of biodiesel contamination on oxidation stability of neat and blended fuels was also studied by conducting test ASTM D2274. In addition, the influence of biodiesel contamination on physicochemical properties after stressing the fuel was investigated according to the ASTM methods. The presence of biodiesel at contaminant levels did not have significant effects on the fuel properties or storage and oxidation stability of neat and blended HRD-76 or F-76. Properties of contaminated samples were determined to meet MIL-DTL-16884N specifications. The storage stability of the HRD-76/B100 blends was also investigated on the basis of the ASTM D5304 method.