Endocellular bacteria being localized or living inside hyphae or spores have been reported for a few fungi and the interactions between bacteria and their host fungus may have potentially beneficial functions. Acremonium strictum Gams. is a filamentous, cosmopolitan fungus with genetically diverse taxon and ecologically diverse distribution. As a polyphagous fungicolous fungus, it is able to overgrow many other fungi though it shows commensalism interactions with Psilocybe fasciata, a psychoactive mushroom as a companion fungus. Two types of bacteria, a coccobacillus and a long bacillus were accidentally observed to be released from the disruptive gap near the dilatate tip of hyphal cell of A. strictum by scanning electron microscope when studying the interactions between P. fasciata and A. strictum. The existence of these endobacteria was further confirmed by fluorescence microscopy. In the present study, two endocellular bacteria, Acinetobacter sp. Epbas6 and Bacillus licheniformis, were isolated from hyphae of A. strictum and identified on the basis of their morphological and biochemical characteristics combined with sequence analysis of 16S rDNA. The pattern of population succession of these two bacteria during their host strain storage was also preliminarily investigated. The ratio of these two bacteria was about 77.5 to 1 based on micrographical and statistic analysis of colony numbers from the original isolates. However, in isolates of fungus preserved at 4℃ for 6 months, B. licheniformis predominated over Acinetobacter sp. Epbas6 with the ratio being 50.45 to 1. Only B. licheniformis was observed in isolates of A. strictum preserved at 4℃ for 12 months. Consistent with above results, the 16S rDNA sequences of both bacteria were able to be detected by multiplex PCR using specific primers from the isolate of A. strictum preserved at 4℃ for 6 months while only that of B. licheniformis was amplified from the isolate preserved at 4℃ for 12 months. These results suggest that a complex interaction might exist between the two endocellular bacteria resulting in a dynamic population succession in hyphal cells of their host fungus during spawn preservation at 4℃. Although results described here might not be an actual reflection of natural state, they provide some clues as to what really happens in a complicated natural environment. Physiological and ecological characteristics e.g. nitrogen fixation, production of antibiotic substances, degradation of lignocellulose and adaptability to extreme environmental conditions etc. of Acinetobacter sp. Epbas6 and B. lichenoformis warrant further study to systematically understand the interactions between these intracellular bacteria and their host fungus.