The purpose of this paper is to design a logical model of an information system for the sale of used personal cars. To create and understand such a model it is essential to analyse the business system, its key characteristics, business functions, global processes etc. Gathering and organizing quality information and data is also a critical factor in the development of such a system. The first part of the paper is based on the theory that is the basis for the development of the model. It presents and explains in more detail concepts such as information system, processes, functions, data flow diagram, data modelling, normalization. The second part of the paper presents the development of a logical model of an information system for the sale of used personal cars. The first step was the analysis of the system for the sale of used cars, including all legal regulations. The second step was modelling the processes that arise during the sale, and the third and final step was the design of a data model. By designing a data model, a conceptual (ER) model was created, which was subsequently translated into a relational model. Data normalization was carried out, and finally, basic algorithms for obtaining the most important information from the relational model were presented.