Our recent studies confirmed that the HBV RNAs present in the serum of chronic hepatitis B(CHB)patients are pregenomic RNAs(pgRNAs)with a size of 3.5 kb. These pgRNAs are located in virus-like particles whose morphological structure is similar to that of Dan particles. Since pgRNAs can only be transcribed from the covalently closed circular DNA(cccDNA)located in the nuclear of infected hepatocytes, and the production of pgRNAs is not affected by nucleos(t)ide analogues(NUCs), the presence of viral RNA in serum can reflect the presence of cccDNA in hepatocytes and its transcriptional activity in patients treated with medication. It can be inferred that serum viral RNA can be used as a potential index for safe withdrawal of NUCs. Our results based on a small-sample cohort show that the presence of HBV RNA in serum at the time of drugs withdrawal is indeed associated with virological rebound after drug withdrawal.