The air entrainment in a transient non-evaporating diesel spray was studied using laser Doppler velocimetry, to provide information on the mixing properties in the near-field region extending to 160 nozzle diameters (40 mm). The spray was injected into confined quiescent air at ambient pressure and temperature. The air velocity component normal to a cylindrical surface surrounding the spray was measured during the entire injection period, allowing the instantaneous air mass flow rate and the entrainment rates to be evaluated as a function of time. Two injection conditions were examined and their influence on the entrainment quantified. In the near field zone investigated, the air entrainment in transient liquid jets appears to be lower than that in steady gaseous jets, but larger than that in steady liquid jets.