Optically transparent poly(methyl methacrylate) (PMMA)-based blends with significantly enhanced mechanical and shape memory properties have been successfully prepared via in-situ formation of micro-scale polylactide stereocomplex crystallites (sc-PLA) in the PMMA matrix in this work. To achieve this goal, a certain content of poly(clactide) (PLLA) was firstly melt-blended with PMMA to obtain completely miscible PMMA/PLLA blends, and then an equimolar poly((L)-lactide) (PDLA) was incorporated into the blends, giving rise to the in-situ formation of sc-PLA between PLLA and PDLA. In this way, the micro-scale sc-PLA particles were successfully fabricated and homogeneously dispersed in the PMMA matrix. Consequently, these resultant PMMA/sc-PLA blends possess extremely superior optical transparency, even when the content of sc-PLA reaches up to 12 wt. A further increase in the content of scPLA would lead to the formation of sc-PLA network and aggregation, resulting in the deterioration of optical transparency. Moreover, the incorporation of sc-PLA micro-particles significantly enhances the mechanical property of PMMA and the maximum (approximate to 103 MPa) of these blends demonstrates 50% increase than that (approximate to 70 MPa) of PMMA. More importantly, it has been found that the shape recovery performance of PMMA could be effectively improved by the incorporation of sc-PLA. The optimal shape recovery ratio (86%) and high shape fixing ratio (almost 100%) can be obtained for the PMMAisc12 blend which exhibits excellent optical transparency. It is reasonable to believe that these optically transparent blends with largely enhanced mechanical and shape memory properties possess great application potential in advanced shape memory fields. (C) 2017 Elsevier Ltd. All rights reserved.