The genotypic evolution of HBV quasi-species was analyzed in a nucleoside/nucleotide-naïve patient who developed resistance to entecavir. The lamivudine resistant quasi-species (rtM204V+/-rtL180M), absent at baseline, were emerged as early as 48 weeks after entecavir administration. Entecavir-resistant quasi-species (rtM204V+/-rtL180M plus S202G) were found after week 112 and gradually became the predominant mutations afterwards. The lamivudine- and entecavir-resistant mutations emerged closely in combination with the rtV207L, rtA222T, rtP237T or rtI163V substitutions. Our results indicated that the lamivudine-resistant mutations were developed first and may serve as a prequisite for subsequent entecavir-resistant mutations in this nucleoside/nucleotide-naïve patient.