[Objective] To study the spatiotemporal dynamic of endophytic bacteria numbers in Acanthus illicifolius. [Methods] Annual dynamic of total endophytic bacteria and culturable endophytic bacteria in different organs of A. illicifolius were studied using fluorescence microscopy and plate counting method, respectively. [Results] The number of total endophytic bacteria in roots, stems and leaves was 12.25×107, 7.59×107 and 5.72×107 ind./g(FW) successively. And the number of culturable endophytic bacteria corresponds to 3.98×103, 3.70×103 and 2.18×103 cfu/g(FW). [Conclusion] There were numerous endophytic bacteria in A. illicifolius. The highest concentration of endophytic bacteria was in roots, followed by stems and leaves. Culturable endophytic bacteria accounted for only 0.000 2%?0.146 8% of total endophytic bacteria in A. illicifolius. The fluctuation of the number of total endophytic bacteria and culturable endophytic bacteria in A. illicifolius varied greatly with the change of seasons. The number of total endophytic bacteria in A. illicifolius was highest in summer (July). While the number of culturable endophytic bacteria in A. illicifolius was highest in spring (March).