In South Korea, use of the smart card to pay public transit fares has grown since its introduction in 1996. The proportion of smart card use in Seoul, South Korea, is more than 90% for buses and 75% for Metro. In 2004, the Seoul metropolitan government introduced a new smart card system that has a distance-based fare system, which requires the input of detailed user data, such as boarding time and Global Positioning System-based vehicle location. To investigate the reliability of smart card data, the number of users of every Metro station in Seoul, gathered from smart card data, was directly compared with data obtained from the Seoul Metro Company. By using two simple manipulations to include daily variations and the number of cash users, smart card data appear to be statistically similar to the surveyed data obtained from the Seoul Metro Company. By analyzing the line-specific proportions of smart card use rather than the average smart card use, the accuracy of the results is improved. From the results, it can be seen that smart card data show potential as a basis for describing the characteristics of public transit users, such as the number of transfers, boarding time, hourly trip distribution of the number of trips for different transit modes, and travel time distribution for all transit modes and user types.