Abstract:[Objective] The purpose of this study was to study the distribution, diversity and cytotoxic activity of endophytic bacteria of Sonneratia apetala collected from Maowei Sea, Qinzhou city. [Methods] The 16S rRNA gene sequencing and MTT were used to explore the diversity and cytotoxic activity of endophytic bacteria isolated from different organs and tissues of Sonneratia apetala. [Results] Total of 38 isolates were obtained. The result of diversity analysis showed that these isolates could be phylogenetically classified into 21 genera and 12 families, based on their 16S rRNA gene sequencing. Of them 5 were potential new genera or new genus. Five strains (R74, R71, S92, S85 and S84) had cytotoxic activity against human liver carcinoma Hep G2 cell line. [Conclusion] Endophytic bacteria of Sonneratia apetala are genetically diverse and most of them have abundant new bioactivities.