Control of bioreactors has achieved importance in the recent years. They are difficult to control, which may be attributed to its nonlinear dynamic behavior. The model parameters of the bioreactor also vary in an unpredictable manner. The complexity of the biochemical processes inhibits the accurate modeling and also the lack of suitable sensors makes the process stability difficult to characterize. This paper is mainly concerned in controlling the bioreactors using analog and digital controllers. The bioreactor system is unstable. This unstable system was stabilized and digital controller such as dead-beat and dahlin controllers were implemented. Then the unstable system was considered as it is and various PID controller-tuning methods were studied. The performance of the proposed control strategy is simulated using SIMLINK ver 2.0 in the MATLAB platform and TUTSIM. This methodology can be implemented without any difficulties, and does not show any overshoot and it is quite robust.