One of the methods to control Nano/pico-satellite's attitude is using magneto-torquers as attitude actuators. ITB, at the moment is planning to develop a cubesat. Therefore, the objective of the research was to investigate the performance of such attitude control system for 3U class cubesat. The research used Matlab/simulink-based satellite simulator developed by LAPAN and ITB, and B-dot control law. The advantages of the method are that the actuators are small and lighter compared to the other type of actuators, such as momentum wheels or reaction wheels. However, the disadvantages is that the torques can be created only when the actuator oriented at non-zero angle with local magnetic field. The results showed that the attitude control system could performed the detumbling operation, with the best transient time at about two orbits period. Varying the gain parameter in the controller may result into variation of transient time and even unstability.