The article is devoted to the history of fight against corruption in Russian Empire in XVIII. The author analyzes the materials of investigations of official malfeasances committed by St Petersburg port customs employees. These investigations were carried out by the Governing Senate’s committee of inquiry in the 1740s and resulted in disclosing an organized criminal group of 10 middle and low ranking customs officials and 19 foreign merchants. Besides, 24 foreign merchants occasionally asked the corrupt officials for services. That criminal activity in 1735—1742 caused material damage to the country amounting to 5 or 7% of due customs taxes and duties. The investigation revealed one of the most outstanding corruption cases in the XVIII century. The author discloses the reasons for abuses and conditions that led to the creation of the corruption scheme. Special attention is paid to the characteristics of methods and progress of the investigation and its results. Historical lessons for further development of customs clearance procedures in sea trade of Russia have been outlined. The research work is based on the materials of Russian State Archive of Ancient Acts (Moscow).