A series of well-controlled polystyrene-b-poly(n-butyl acrylate)-b-polystyrene (SAS) triblock copolymers were prepared by emulsion polymerization with a carefully designed amphiphilic macroRAFT (reversible addition-fragmentation chain transfer) agent. The tensile strength of SAS decreased and elongation at break increased, and the Izod impact strength of SAS increased, as the poly(n-butyl acrylate) soft segment content, lower than 40 wt.% for polystyrene toughened, increased. The tensile fracture morphologies of SAS samples further testified the ductile fracture mechanism. The dynamic mechanical analysis (DMA) revealed that there are two glass transition temperatures and two fast modulus-decreasing stages for SAS samples when the temperature increased from -80 ℃ to 140 ℃. The SAS samples have the high transmittance of visible light, the good thermal stability and the low water adsorption. Keywords: RAFT emulsion polymerization; block copolymer; Structure and property *Corresponding Author: Jingxin Lei; Email: jxlei@scu.edu.cn