This article presents final technical and economical results of the comprehensive control rehabilitation project done for the ammonia synthesis plant at JP Nawozy, GA ZAK S.A. The project included the following activities: review of the existing control philosophies and instrumentation infrastructure, design and implementation of the new control loop templates, and tuning of the revised controls over the entire installation. These activities improved installation operation with much more reliable and repeatable dynamic responses. Simultaneously, the overall installation efficiency has been also increased. This initiative is considered as the prerequisite for further control system upgrade with use of advanced process control and process optimization.