||In this thesis, we introduce particle-based conductive composites synthesized by mixing conductive nano/micrometer-sized particles with polydimethylsiloxane (PDMS) matrix. Experiments show that such composites exhibit excellent conductivity as well as good mechanical and thermal properties. By using micro molding and softlithographic techniques, these composites can be patterned into two-dimensional and three-dimensional conducting microstrucures that can be integrated into PDMS-based microchips for wide microfluidic functionalities. Based on such composites, a series of microfluidic devices have been designed and implemented, such as microheater, paperlike thermochromic display and micro thermoindicator. Furthermore, magnetically responsive elastic microspheres shaped into either core-shell or solid structure and consisting of PDMS and magnetic nano/micro-particles, are fabricated by a microfluidic flow-focusing device. Measured by a modified electronic balance, an appreciable magnetostrictive effect of the two types of spherical elastomers is exhibited. Owing to the smart controllability by an external magnetic field from magnetic particles as well as bio-compatibility and non-toxicity of PDMS, these microspherical elastomers may have potential application in drug delivery and release.