Polymerized ionic liquid containing block structure (PIL) has been used as regulator for the phase structure of poly(lactide) (PLA)/poly(ε-caprolactone) (PCL) blends. The phase structure, crystallization, rheology behavior and mechanical properties of PLA/PCL and PLA/PCL/PIL blends were systematically investigated. PIL could be located in PCL phase or at the PLA/PCL interface, enhancing the interaction between polymer components. The crystallization ability of PLA and PCL was simultaneously enhanced with the addition of PIL, since the plasticization effect of ionic moiety and PEO segments in PIL as well as the nucleation effect of PIL-formed ionic cluster. When PIL content was 0.5 wt%, the PLA/PCL/0.5PIL blend system exhibited much better mechanical properties than additive-free PLA/PCL blend. But as PIL contents increased, the significantly change in viscosity ratio between PLA and PCL would lead to obviously change in phase structure of PLA/PCL blend, thus the mechanical properties of the blends would be degraded.