Display omitted •Synthesis of starch capped ZnS nanoparticles following green chemistry principles.•Starch capping ensured by TEM, HRTEM and FTIR studies.•Quantum size effects observed in optical absorption studies.•Progressive quenching of surface states with starch addition observed in PL spectra. Following a green synthesis method, zinc sulfide (ZnS) nanoparticles were prepared by chemical co-precipitation technique using starch as capping agent. Microwave irradiation was used as heating source. X-ray diffraction studies indicated that nanopowders obtained were polycrystalline possessing ZnS simple cubic structure. Transmission electron microscopic studies indicated that starch limits the agglomeration by steric stabilization. Interaction between ZnS and starch was confirmed by Fourier transform infrared spectroscopy as well as Raman scattering studies. Quantum size effects were observed in optical absorption studies while quenching of defect states on nanoparticles was improved with increase in starch addition as indicated by photoluminescence spectra.