Fossil fuel reserves are being depleted due to increasing energy requirements. One of the solutions is to partly replace fossil fuel by renewable biodiesel fuel. However, the physical properties of biodiesel fuels need to be thoroughly investigated before applying biodiesel or diesel-biodiesel blends in diesel engines, in order to improve the combustion efficiency.This paper presents the experimental study of diesel fuel and biodiesel blends on injection flow characteristics and fuel spray behavior. Seven fuels were tested: diesel fuel, five diesel-biodiesel blends: 10%(B10), 20%(B20), 30%(B30), 40%(B40), 50%(B50), and pure biodiesel(B100) in a diesel engine equipped with a piezo injector. Injection pressures were set at 30-180 MPa for the study of the injection flow characteristics and at 30-150 MPa for the study of spray behavior in non-vaporizing conditions. The experimental results show that the injection flow characteristics and fuel spray behavior are the same with biodiesel blends as with diesel fuel. With pure biodiesel (B100), which has a density that is 5.2% higher and a viscosity 50% higher than diesel fuel, the discharge coefficient decreases by 3.63% but at injection pressure values of over 55 MPa, the effect on the discharge coefficient is insignificant. At the beginning of the injection period (up to 2000μs), the spray penetration and spray angle of B100 are different but after 2000 μs the spray behavior is similar to that of the other fuels. Correlations based on the work of Payri et al., Soteriou et al. and Naber & Siebers were used for comparison with the experimental data.