In Biodiesel Fuel Research Working Group(WG) of Japan Auto-Oil Program(JATOP), some impacts of high biodiesel blends have been investigated from the viewpoints of fuel properties, stability, emissions, exhaust aftertreatment systems, cold driveability, mixing in engine oils, durability/reliability and so on. In the impact on exhaust emissions, the impact of high biodiesel blends into diesel fuel on diesel emissions was evaluated. The wide variety of biodiesel blendstock, which included not only some kinds of fatty acid methyl esters(FAME) but also hydrofined biodiesel(HBD) and Fischer-Tropsch diesel fuel(FTD), were selected to evaluate. The main blend level evaluated was 5, 10 and 20% and the higher blend level over 20% was also evaluated in some tests. The main advanced technologies for exhaust aftertreatment systems were diesel particulate filter(DPF), Urea selective catalytic reduction (Urea-SCR) and the combination of DPF and NOx storage reduction catalyst(NSR). The analysis items were regulated exhaust gases such as CO, HC, NOx, PM, fuel consumption rate and unregulated exhaust emissions. It was revealed that the level of regulated exhaust emissions from catalyst-out was very low regardless of the types of biodiesel blendstock and advanced exhaust aftertreatment systems until 20% of biodiesel blends. It was also revealed that NOx emissions from both engine-out and catalyst-out increased a little by 20% of FAME blends. Moreover, NOx emissions from catalyst-out remarkably increased by more than 20% of FAME blends. On the other hand, it was concerned that the higher FAME blends led to raise catalyst temperature of DPF/NSR when additional amount of fuels from the exhaust pipe was injected to recover from sulfur poisoning, in spite of the lower heating value of FAME blendstock than that of base diesel fuel.