[Objectives] To determine the composition of culturable bacteria, and screen cellulolytic bacteria, in the intestine of Spodoptera frugiperda larvae. [Methods]  The traditional bacterial culture method and the 16S rDNA molecular marker were used to identify culturable bacteria in the intestine of S. frugiperda larvae. Congo red staining was used to screen cellulolytic bacteria, and cellulase activity was determined with the 3,5-dinitrosalicylic acid (DNS) method under different pH (5.0-9.0). [Results] Fourteen intestinal bacterial strains were isolated, including Glutamicibacter, Enterococcus, Bacillus, Staphylococcus, Morganella, Enterobacter, Shigella, Cronobacter, Klebsiella, Serratia and Ochrobactrum, which belong to eleven genera of three phyla; Actinobacteria, Firmicutes and Proteobacteria. Among these, two cellulolytic bacteria strains from the Bacillus genus of Firmicutes were identified. The results show that the cellulase activities of these two cellulolytic strains were relatively higher under pH 5.0-8.0 and peaked at pH 8.0. [Conclusion]  The intestine of S. frugiperda larvae contains a diversity of bacteria. The cellulase activity of cellulolytic strains was significantly higher under alkaline than under acid conditions. These results provide new information on cellulolytic bacteria, and contribute to their use in feed production, food processing and chemical energy. In addition, beneficial intestinal bacteria are expected to become a new target for controlling S. frugiperda which is now a major global pest.