Here we used wet chemical method to grow zinc sulphide nanoparticles (ZnS NPs). HRTEM and XRD pattern were used for structural characterization. The Phase of the ZnS NP unit cell was cubic and the average crystal size is found to be ≈15 nm. The defect state related photoluminescence spectrum showed visible emission of ZnS NPs. We used optical spectroscopy like UV–VIS and fluorescence spectra, HRTEM images and FESEM images to study the interaction and the formation of bioconjugate of Lysozyme and ZnS NPs. Our result showed occurance of spontaneous binding process between Trp of the Lysozyme and ZnS NPs. Formation of ground state complex with small red shift of the absorption peak of Lysozyme is observed due to binding of the Lysozyme with ZnS NPs. Zinc Sulphide nanoparticles quench the fluorescence emission of tryptophan in the Lysozyme. We calculate the Stern–Volmer quenching constant and the number of binding sites.