The need for diversification of energy sources and reducing various emissions including CO(2) emission in diesel engine can be met with alternative diesel fuels such as gas to liquid (GTL) and GTL-biodiesel blends. But there should be a clear understanding of the combustion and engine-out emission characteristics for alternative fuels. In this respect, an experimental study was conducted on a 2.0 L 4 cylinders turbocharged diesel engine fuelled with those alternative diesel fuels to investigate the engine-out emission characteristics under various steady-state engine operating conditions. The results revealed that noticeable decreases in THC (22-56%) and CO (16-52%) emissions for GTL-biodiesel blends were observed, whereas NO(x) emissions for GTL-biodiesel blends increased by a maximum of 12% compared to diesel. With regard to particle size distributions (PSDs) for GTL-biodiesel blends, the particulate matter (PM) number concentration in accumulation mode decreased, as a result of the excess oxygen content in biodiesel. Contrary to the tendency in the accumulation mode, there was a slight increase in the PM number concentration in the nucleation mode under the operating conditions wherein the exhaust gas recirculation (EGR) strategy was applied. The total PM number concentration for G + BD40 decreased by a maximum of 46% compared to that for diesel. From these results of enhanced emission characteristics compared to diesel and GTL fuel, the potential for the use of GTL-biodiesel blends could be confirmed. (C) 2010 Elsevier Ltd. All rights reserved.