A type of newcastle disease virus (NDV) immunosensor based on 81° tilted fiber grating (81°-TFG) is proposed. The basic principle and sensing properties of the 81°-TFG are briefly analyzed. Staphylococcus aureus protein A (SPA) is used to modify the surface of 81°-TFG, and then highly purified NDV monoclonal antibodies (MAbs) are immobilized on 81°-TFG surface through SPA molecules. Finally, the NDV immunosensor is successfully developed. The experimental results show that the immunosensor has a lowest limit of detection to NDV of between 0.1 ng/mL and 0.2 ng/mL, gets saturated at about 1.0 ng/mL, and has good linearity with R2 of about 0.982 and sensitivity of about 342 pm/(ng·mL -1) in the concentration range from 0 to 1.0 ng/mL. In addition, this immunosensor shows good reusability and high specificity to NDV, and can also be used in clinical test for NDV. Compared with the traditional biochemical methods such as immunofluorescence technique, enzyme-linked immunoabsorbent assay, this technique proposed in this paper has the advantages of no mark, simple operation, fast detection.