Termites are worldwide pests causing considerable damage to agriculture, forestry and buildings. Although physical and chemical methods have been tried to eliminate termite populations, they have the limitations such as low effectiveness, high-toxicity residue, environmentally harmful and high cost. Therefore, it has attracted much attention to develop highly effective, low-toxicity, long residual period, environmental friendly and low-cost termiticides. Here, we report the characterization andnitrogen fixation activities of a nitrogen fixation endophytic bacterium, strain HDZK-BYTG4, isolated from O. formosanus. The morphology and physiochemical characteristics of HDZK-BYTG4were very similar to that of Klebsiella pneumoniae. Analysis of 16S rDNA gene sequence showed that strain HDZK-BYTG4 exhibited >99 % sequence similarity to K. pneumoniae. Combining above phenotypic and phylogenetic properties, strain HDZK-BYTG4 was identified as K. pneumoniae. Strain HDZK-BYTG4 had nitrogen ûxation activities to apparently complement the termite’s nitrogen deficient diet and HDZK-BYTG4 produced signiûcant amounts of ammonia when it was grown on nitrogen deûcient medium under anaerobic condition. These results provided the basis for studying the nitrogen-fixing mechanisms in the termite gut and facilitated the development of nitrogen-fixing microorganism resources.The objective of this study was to isolate, identify, and characterize facultative anaerobic bacteria in the gut of O. formosanus and their possible role of facilitating the development of nitrogen-fixing microorganism resources.