Air quality standards set forth by the Clean Air Act and its amendments have established guidelines for reduction of harmful ground level emissions from the aviation sector. Biodiesel, defined as the mono–alkyl esters of fatty acids derived from vegetable oil or animal fat, in application as an extender for combustion in compression ignition (diesel) engines, has demonstrated a number of promising characteristics including reduction of exhaust emissions. This work examines the fuel properties of BioJet fuel blends consisting of 0.10–0.30 vol. frac. methyl soyate (SME) in JP–8 and in JP–8+100 jet fuels. Testing of cold flow properties indicated that blends with as little as 0.10 vol. frac. SME may limit operation of aircraft to lower altitudes where ambient temperature remains warmer than –29 C. Treatment of SME with cold flow improver additives may decrease this limit to –37 C. Blends with winterized SME gave the best results, reducing the limit to as low as –47 C, a value that meets the standard fuel specification for JP–8. Water reactivity studies indicated that SME/JP–8 blends absorbed very little water from buffered solution following contact with the oil phase. Although interface ratings for blends with up to 0.50 vol. frac. SME were “1b” (clear bubbles covering not more than 50% of the interface) or better, separation ratings no better than “(3)” (formation of cloudy suspensions in the oil layer) were observed. Even though fatty derivatives such as biodiesel undergo oxidative degradation more readily than jet fuels, careful production, transport, and storage of BioJet fuels should not present a significant problem.