The measurement of spray penetration length is one of crucial tasks for understanding the characteristics of diesel spray and combustion. For this reason, many researchers have devised various measurement techniques, including Mie scattering, schlieren photography, and laser induced exciplex fluorescence (LIEF). However, the requirements of expensive lasers, complicated optics, delicate setups, and tracers that affect fuel characteristics have been disadvantages of previous techniques.In this study, the background-oriented schlieren (BOS) technique is employed to measure the vapor penetration length of diesel spray for the first time. The BOS technique has a number of benefits over the previous techniques because of its quantitative, non-intrusive nature which does not require lasers, mirrors, optical filters, or fuel tracers. The objectives of this study are to establish the BOS technique as a viable method and then to use it to measure the vapor penetration of diesel spray as a function of ambient temperature, pressure, and orifice pressure drop by using BOS technique after verifying the possibility as a new useful method.The experiments were performed on an optically accessible, constant-volume pre-combustion type chamber (CVPC) simulating the ambient conditions within a diesel engine. A single-hole solenoid injector and a common rail system were used for fuel injection. The structured background with randomly generated dots was taken by a high speed CCD camera, and the images were post-processed by analysis programs. The schlieren images were also taken under the same set of conditions to validate the results of the BOS technique. The BOS results show a good agreement with the schlieren results in terms of vapor penetration. It is worthwhile to develop a more convenient and quantitative diagnostic technique applicable for investigating the penetration characteristics of diesel spray and capable of providing fundamental information to the area of CFD study.