The population diversity of progeny viruses of Kyuri green mottle mosaic virus (KGMMV) in consecutive serial passages in two systemic hosts, zucchini squash and cucumber plants, established from genetically identical viral RNA, was examined in this study. An initial plant was inoculated with in vitro transcripts from a full-length cDNA clone of KGMMV. The initial viral population (passage 0) was transferred five times in parallel populations in the same hosts species for analysis of progenies of KGMMV. The percentage of mutations of progeny viruses fluctuated slightly, as expected, during the serial passage, and these results did not correlated with the mutation frequency calculated as the total number of mutation observed in all the clones sequenced for a given viral population were divided by the total number of bases sequenced for the population. The mutation frequencies represented similar distributions over the course of serial passages in the two systemic host plants. Seventeen unique mutations were detected from a total of 40 clones (19,120 bases) sequenced, indicating a relatively small overall mutation rate of 17 nucleotide substitutions. The majority of observed mutations in the viral populations consisted of substitutions: 61.60 and 64.08% of the mutations in cucumber and zucchini populations, respectively. The types of transitions and silent mutations indicated that progenies of KGMMV reached stabilized selection during the host passages and maintained viral quasispecies in systemic hosts.