The behavior of postimpingement diesel spray was investigated by comparison with that of a steady gas jet. Diesel sprays having various injection rates were injected into a high-pressure chamber. From high-speed photographs of the impinging process of the spray, the velocities just before and after impingement were analyzed as a function of the wall distance. The penetration coefficient of a postimpingement spray is defined and compared with that estimated by a simple momentum theory of a gaseous jet. Also, the effects of injection rate and its period on the penetration coefficient are discussed. Velocity deceleration occurred at the impingement point, controlled more by the impingement distance than by the injection period or the ambient pressure. Also, the characteristics of the diesel spray became nearer to those of the steady gaseous jets as the injection period became long. It is considered that the momentum loss caused by the wall friction is greater for the postimpingement spray than for the radial gaseous jet.