4D printing is known as the integration of 3D printing technologies with active smart materials. To achieve the movement, shape memory effect (SME) is often utilized in 4D printing to recover the smart material from a temporary shape to its pre-determined configuration. 4D printed materials were usually fabricated from stereolithography (SLA) printers by using the photopolymerization techniques. Currently, little 4D printing research focus was given to the commercially available fused deposition modelling (FDM) printers and thermoplastic materials. Polylactic acid (PLA) is a well-known and market-ready material for FDM 3D printer. However, it is high brittle thus is less suitable to be used in 4D printing applications. In this study, we demonstrated that the plasticizing effect can be utilized to alter the behaviour of PLA thus to achieve 4D actuation movement. By incorporating different amount of poly(ethylene glycol) (PEG) plasticizer, the thermo-mechanical behaviour and the microstructures of the PLA can be modified. For example, significant decreases in the glass transitional temperature (Tg) of the PLA can be observed due to the enhanced polymer chain interaction. The ability to modify the actuation temperature of the 4D printed PLA composites allows for the material to be used in a variety of applications.