The objective of this work is to study the fundamental knowledge for the disintegrating process and the characteristics of a diesel spray. Break-up length of a high speed jet in a pressurized vessel was measured by an electric resistance method. Spray angle and spray tip penetration were investigated photographically, A laser diffraction method was used for measuring the Sauter mean diameter.The spray tip penetration is first proportional to a time, and after that, it is proportional to a root of the time from a beginning of an injection. The length in this first stage is considered to be equivalent to the break-up length of a fuel jet. The maximum spray angle is observed at a ratio of nozzle length to diameter being about 4. The spray angle decreases with increasing viscosity. The Sauter mean diameter gradually increases as the spray angle decreases.