The state-space model is identified using the identification tool of MATLAB, and the best fit of 99% of measured and simulated data was obtained. Further, state-space model was converted to a transfer function model and finally simplified to an unstable second order time-delay transfer function model. Internal model control based proportional integral derivative (IMC-PID) controller design method was proposed for unstable second order time delay with RHP zero (USOPDT) and successfully tested to the nonlinear bioreactor process model. The temperature of the bioreactor was successfully controlled by proposed controller in both cases setpoint and disturbance change. The performance of the controller was evaluated in terms of IAE, ISE, ITAE and the corresponding values of 20.99, 49.02 and 292.50 were obtained respectively. Proposed method shows better closed-loop performance in terms of IAE and settling time than the other reported methods for temperature control of bioreactor.