Despite several attempts to synthesize water-expandable polystyrene (WEPS) beads, the product is still far from commercialization. This is mainly due to the inability of the PS beads to preserve the blowing agent (water) during storage, which leads to the loss of expandability. We report a new generation of WEPS beads with extended shelf life and good expandability. The beads were synthesized through Pickering emulsion polymerization in which cross-linked starch nanoparticles (CSTNs) were used as a water-stabilizing agent. Synthesized beads with different CSTN content could encapsulate 5.0-12 wt % of the water droplets of 3-4 mu m in diameter. Thermogravirnetric analysis showed that the entrapped water is mainly bound water with a strong adsorption to the starch nanopartides. Over 88% of the initial bound water content can be preserved 3 months after synthesis, thereby prolonging the shelf life of the CSTNWEPS beads. The expansion behavior of CSTNWEPS beads was investigated in hot oil and at an optimized temperature of 135 degrees C. The best results (expansion ratio of similar to 7 for as-synthesized beads and similar to 3 after 3 months) were obtained for the sample containing 1 wt % of CSTN and 5.6 wt % of water in the form of uniformly distributed microdroplets. Finally, the morphological investigation of the expanded beads revealed that the CSTNs not only stabilize the water microdroplets in the beads but also reinforce the foam during expansion and inhibit cell wall rupture.