Hepatitis delta virus (HDV) is encapsidated by the envelope proteins of hepatitis B virus (HBV). The major HBV lamivudine (LMV)-resistant mutations in the polymerase gene within the reverse transcriptase (rt) region at rtM204V or rtM204I are associated with changes in the overlapping envelope gene products, in particular, the gene encoding small envelope protein (s) at sI195M or sW196L/S/Stop. We have demonstrated that the LMV resistance mutations corresponding to sW196L/S inhibited secretion of HDV particles, while changes corresponding to sI195M did not affect secretion. Differential efficiencies of HBsAg proteins expressed by LMV-resistant HBV to support HDV secretion may have consequences for clinical prognosis as coinfected patients are treated with antiviral agents.