Sauter mean diameter and air-entrainment characteristics of nonevaporating unsteady dense sprays are measured by means of an image analysis technique which uses an instantaneous shadow picture of the spray and amount of injected fuel. Influences of injection pressure and ambient gas density on Sauter mean diameter and air entrainment are investigated parametrically. An empirical equation for the Sauter mean diameter is proposed based on a dimensionless analysis of the experimental results in which Sauter mean diameter decreases with an increase in injection pressure and a decrease in ambient gas density. It is also shown that the air-entrainment characteristics can be predicted from the quasi-steady jet theory.