In this paper, a high-resolution visualization technique has been used in order to characterize Diesel spray structure in the near-nozzle field. For this purpose, three conical nozzles with different diameters have been used to relate nozzle geometry and spray behavior in non-cavitating conditions. As a first step, geometrical and hydraulic characterization of the nozzles has been performed. The analysis of the images obtained has shown that spray aperture varied significantly during the first millimeters of the spray, until reaching to the stabilized value of spray cone angle, which is the one usually characterized by other visualization techniques. Furthermore, the structure of the liquid gas interface presented an oscillatory behavior, which is related to primary atomization process. These oscillations have been quantified and statistically correlated with nozzle geometry and operating conditions by means of three different non-dimensional numbers: Reynolds number, air/fuel density ratio, and Ohnesorge number.