Ancient silk has important historical, artistic, and scientific value, and its origin and spread have always been a research hotspot. However, traditional analytical methods have encountered great challenges in the analysis of ancient silk microtraces due to the problems of large sample consumption, serious contamination, and degradation. To overcome this problem, a taxonomically specific anti-fibroin monoclonal antibody was designed and successfully prepared by animal immunization, and a novel photoelectrochemical immunosensor based on the antibody and ZnO nanowires array was constructed for the first time. This photoelectrochemical immunosensor possessed a detection limit as low as 0.56 ng mL−1 and a linear range from 1 to 1000 ng mL−1, showing great potential in the ultrasensitive detection of silk trace. In addition, the elaborate immunosensor demonstrated preeminent performances in the specificity, stability, and reproducibility, especially in the qualitative and quantitative detection of soil samples extracted from Sanxingdui archeological sites. Therefore, the proposed method not only provides a powerful analytical tool for exploring the origin and spread of ancient silk but also provides a reference for the study of other types of protein artifacts.