It is challenging to fabricate uniform starch microspheres (SMs) with sub-10 μm diameters in starch-polyethylene glycol (PEG) aqueous two-phase system (ATPS). To address this issue, a refined approach using starch-polyvinylpyrrolidone (PVP) ATPS is presented in this work. Phase diagrams were constructed for ATPSs containing PVPs of varying molecular weights, which provided crucial insights into the influence of PVP on SM formation. The results revealed that increasing both the molecular weight and concentration of PVP led to higher starch and PVP contents within the dispersed phase, significantly influencing the final yield of SMs. The morphology, size, crystallinity, and swelling behavior of SMs prepared in the starch-PVP ATPS were comprehensively characterized. Increasing PVP molecular weight resulted in smaller SMs with enhanced crystallinity and reduced swelling capacity. Notably, SMs prepared with 58 kDa PVP exhibited an average particle size (D