Background/Objectives: When conventional PI controllers are used to control non linear processes, the controllers must be tuned very conservatively in order to provide stable behavior over the range of operating conditions. The conservative controller tuning can result in serious degradation of control system performance. Therefore it is necessary to go for optimizing techniques. Methods/Statistical Analysis: In this paper a modified approach of firefly algorithm is compared with the firefly algorithm. The modified approach is derived from the impact of the tuning parameters over the objective function peak overshoot. This modified approach using firefly algorithm is validated through simulation results. The transfer functions employed here are stable second order system, second order with inverse response and higher order systems, particularly non minimum phase systems. Findings: For the stable second order systems and for the higher order non minimum phase systems the modified approach based on firefly algorithm outperforms the existing firefly algorithm. The modified approach not only reduces the considered objective functions such as PO, ITAE but also the other functions such as ITAE and settling time. Application/Improvements: The modified approach can also be extended for unstable systems. The modified approach is discussed with third order systems here. However it can be extended for still higher order systems.