A distributed expert control system (DECSHZ) has been built for a hydrometallurgical zinc process, whose basic steps arc leaching, purification and electrolysis. It consists of a central computer management system and three local expert control systems, one for each of the basic steps. This paper deals with the design and application of DECSHZ, especially its distributed architecture and main functions: expert control strategies based on rule models and a combination of rule models and steady-state mathematical models: system implementation; and the results of actual runs. DECSHZ has been found to provide not only a very pure product, but also significant economic benefits.