Abstract: A method and a system for prophesying a behavior of an online gamer, and a computer program product thereof are provided. In the present method, a gamer descriptor of a specific gamer of an online game accumulated before a time point is obtained firstly. Then, the gamer descriptor is divided into a plurality of sub-traces according to the time. Thereafter, at least one feature is derived from each of the sub-traces, and all features derived from the sub-traces are used for determining a possibility that the specific gamer quits the online game within a specific time period in the future.