© 2017 IEEE. The two-stage continuous bioreactor system is an advanced configuration that could improve process production and system performance. Our paper studies the problem of feedback stabilization of this system. Based on a simple dynamic model, a constant-yield controller is derived to stabilize the system. Using Lyapunov stability analysis, this control law is proved to be able to regulate the system at the design steady state with stability basin the entire positive orthant. The control law is also proved to be robust to errors in influent concentration, in the sense of preserving the stability region.