OBJECTIVE: To establish a reliable molecular diagnostic system for precise identification of BK virus (BKV)-associated pathologies. METHODS: We designed a set of in-situ hybridization (ISH) probes targeting two conserved sequences within the large T antigen region of BKV, exhibiting highly specificity from JC virus and SV40 homologs. By integrating the branched DNA signal amplification technology with these probes, we developed a novel ViewRNA-ISH detection system. RESULTS: The optimized BKV-LT ViewRNA-ISH system demonstrated enhanced diagnostic specificity and sensitivity compared to conventional immunohistochemical methods in both cellular models and clinical specimens. Validation using 29 clinical samples and 3 subcutaneous planted tumor samples revealed 93.75 % (30/32) concordance with IHC findings, with 2 previously IHC-negative renal biopsies showing positive signals through ViewRNA-ISH detection. CONCLUSIONS: Our BKV-LT ViewRNA-ISH system enables dual-mode (fluorescent/ chemical) detection of BKV nucleic acids, providing superior diagnostic performance for BKV-associated pathologies with potential clinical utility in renal allograft monitoring.