The interaction between norfloxacin (NRF) and ovalbumin (OVA) was studied by fluorescence and absorption spectroscopy.The binding constants and the binding sites were measured by fluorescence quenching method.It was found that the emission peak of OVA was positioned at 338 nm.When the norfloxacin was added into OVA solution gradually,the intensity of 338 nm emission peak of OVA decreased obviously and moved towards long wavelength.The experiment demonstrated that the higher the temperature,the lower the slopes of quenching curves of OVA in the presence of different amounts of NRF.It was confirmed that the combination of NRF with OVA is a single static quenching process.With the increase in the pH of the solution,the quenching efficiency decreased in the binding.From thermodynamic parameters,it can be judged that the binding power between OVA and NRF is electrostatic effect and H-bond formation.The UV-Vis absorption spectra of OVA in the presence of NRF show that the conformation of OVA changed.