We propose novel biomimetic polymer microactuators. The actuation mechanism is inspired by nastic movement of the moving plant, Mimosa pudica, which folds its leaves upon external stimulus by regulating turgor pressure of cells in specific location. Photo-cured poly(ethylene glycol) diacrylate (PEGDA) microactuator is fabricated using projection micro-stereolithography (PμSL) capable of complex 3D micro fabrication. The swelling effect of PEG in water and organic solvent is exploited as an actuation mechanism of the device. Stress relaxation in the structure due to solvent absorption is controlled locally by delivering solvent through microfluidic channels embedded in the actuator, thereby generating a net movement in the device. Timescale of the motion derived from analytical swelling model suggests that actuation speed can be effectively increased by scaling down the actuator because the characteristic swelling time depends on the length as L2, which is verified experimentally.