This paper deals with the main causes that generate bonded warehousing above the initial deadline -granted by bonded warehouses for the nationalization of the cargo. This research is restricted to the importation processes of a large company, on the oil and gas industry. Considering that the storage figures are paid corresponding to the FOB value of each load, and that the analyzed company's sector was responsible for importing a FOB value of R$ 35,157,935,870.00 in 2017, which represents 4% of Brazil's GDP, an improvement proposal was sought, in order to reduce the company's indexes through the use of the Lean tool. The examination was performed by verifying the company's records in a computerized system, the collected data was then analyzed through the "analysis of the five whys" and categorized into seven main factors. Then, there was a prioritization of analysis of storage causes that were higher than the established time of the most recurrent factors, and suggestions for corrective actions were informed through brainstorming. As a result, a new form of service contracting was indicated for the company in question and several suggestions for improvement in the other causal factors were given. The use of Lean tools in warehousing processes has been the focus of several studies in the academic area, however, the use of Lean in bonded warehousing management processes represents a breakthrough, since the treatment regarding common and bonded warehousing diverges significantly. Furthermore, during the year of 2019, the study's improvement propositions have being applied and are currently in operation. New research in the area can be applied seeking the verification and quantification of the result obtained by the informed suggestions.