AIMS: IL-12B, a subunit of the IL-23 family of cytokines, plays a crucial role in various diseases such as viral infections, autoimmune disorders, and tumors. This study aimed to identify high-affinity nanobodies that bind to distinct epitopes of IL-12B to and assess their potential for therapeutic and diagnostic applications, particularly through fluorescence resonance energy transfer(FRET) to evaluate their ability to target IL-12B. METHODS: IL-12B protein was expressed in eukaryotic cells and used to immunize camels to induce an immune response. Camel-derived anti-IL-12B nanobodies were isolated and screened via phage display to identify those with high specificity and affinity for IL-12B. Binding affinity and epitope interactions were further analyzed using high-performance liquid chromatography (HPLC) and ForteBio Octet assays. A FRET-based assay was developed to evaluate protein interactions for precise therapeutic targeting. RESULTS: Several high-affinity nanobodies targeting IL-12B were successfully generated. These nanobodies exhibited strong binding to various epitopes of IL-12B. Screening by HPLC and ForteBio Octet confirmed their high specificity and affinity, while fluorescence analysis demonstrated efficient energy transfer between thenanobodies, indicating successful interactions. CONCLUSIONS: This study identified high-affinity nanobodies against IL-12B and used FRET to characterize their interactions. These nanobodies show promise for therapeutic potential targeting IL-12B-related diseases, including viral infections, autoimmune disorders, and cancer. However, further clinical studies are needed to fully explore their potential for diagnostic and therapeutic applications.