This paper is concerned with fractional-order PIλDμcontrollers. The definitions and properties of fracti-onal calculus are introduced. The mathematical descriptions of a fractional-order controller and fractionalorder control systems are outlined. The effects on control systems of order variation for fractional-order Piλ Dμ controllers are investigated by qualitative analysis and simulation. The conclusions and simulation examples are given. The results show the fractional-order PIλDμ controller is not sensitive to variation of its order.