In general, game players want their own characters that project themselves to have stronger power and honor in a virtual world. Their aspiration is achieved by pulling up character’s level or accumulating wealth in game. Some players, thus, cheat at games in a variety of ways to skip the repetitive and tedious process of gaining experience and wealth that consumes a considerable amount of time and effort. Cheatings are regarded as harmful behaviors toward both game producers and players in good faith, and if the rate of the cheating players exceeds a certain threshold, the game producers will not be able to provide fair and successful services anymore. Therefore, the game producers make various efforts to detect and impose a sanction on the cheaters. In this paper, we propose a method to estimate population size of the cheaters more quickly and accurately, in a relatively shorter time and lower cost than traditional methods, by using the method which is used frequently by ecologists. Among the various ecological estimation methods, Jolly-Seber estimator, based on capture and recapture method, was selected to estimate the characteristics of players in virtual world. Moreover, the video footage recorded for estimation is expected to become a legal evidence for game producers to impose sanctions such as permanent account suspension. Based on the estimated population size, the ratio of the cheaters among ordinary players can be estimated, and this ratio is expected to help the game producers to make swift decisions on the timing of sanctions. In this paper, we estimate the population size of cheating players in Blade & Soul, a popular MMORPG game. The total number of cheating players was estimated to be 274,639 players in four selected areas. In 2012, according to official press release of the game producer (NCSOFT Corporation), Blade & Soul had 230,000 concurrent users at every second. The number of active users is approximately estimated to be 2,300,000. Using the method proposed in this paper, the rate of cheating players in the game is approximately 11.94%.