Proportional-integral-derivative (PID) control of unified chaotic system (UCS) was researched. For optimization of PID controller's structure and parameners, a parallel genetic algorithm (PGA) was proposed. In GA evolution process, hybri d decimal system and binary system matrix encoding technique was adopted. Simula tion study results of optimal PID control for UCS show that: 1) UCS can be cont rolled to unstable zero equilibrium point by using only one PI controller. 2) U CS can be controlled to any unstable non-zero equilibrium point by using three PI controllers. 3) The proposed PGA owns global optimization ability, it can av oid premature problem of simple GA. 4) The control system obtained good regulat ing performance and strong robustness.