In this paper, the injection characteristics and macroscopic spray behavior of biodiesel and diesel fuel within a common rail system are investigated. The injection rate is measured with Bosch method, spray visualization system is employed to study the macroscopic spray characteristics of both fuels. The results show that the injection delays of biodiesel and diesel are almost the same. Comparing to diesel, injection duration of biodiesel is a little longer and injection fuel quantity is a little larger. The macroscopic spray result shows, with increased injection pressure, the tip penetration of biodiesel becomes longer and the spray cone angle becomes larger. When ambient pressure increases, the injection tip penetration becomes shorter and the spray cone angle becomes larger. Comparing to diesel, injection tip penetration of biodiesel is longer and spray cone angle is smaller, because the kinematic viscosity and surface tension of biodiesel are larger than those of diesel. The difference of spray characteristics of both fuels is no longer obvious under higher injection pressure. With increased ambient pressure, the difference of spray tip penetration of both fuels becomes larger, and the difference of spray cone angle become smaller.