Methane - Oxidizing Bacteria (MOB) are a ubiquitous group of bacteria characterized by a unique ability to use methane as a sole source of carbon and energy. The enrichment cultivation method was used to enhance the growth of MOB. Three new strains of MOB were isolated from effluents of rice paddy and coastal seawater sample，tentatively characterized as Methylocystis MOB. Initial morphological characterization of the three strains showed them as white consistent colonies on mineral medium agar enriched with 0.1M methanol. Scanning electron microscopy demonstrated them as cocci cells arranged in aggregates of 5-20 cells per aggregate，with each cell measuring about 0.5μm in diameter. Biochemical characterization of the three strains showed them to grow optimally at near neutral pH (pH6) and moderate temperature (30℃).Cells of all three isolates were also shown to grow best when no salt was added to the growth media. The three isolates were observed to utilize methanol and formate in addition to methane as carbon source. pmoA gene analysis showed the three strains to share 99.4％ pmoA sequence similarity，and belonging to the Methylocystis cluster of MOB. 16S rDNA sequence analysis confirmed the pmoA gene sequence results that strains m231 and m261 from rice paddy effluents，and. strain ml511 from coastal seawater samples were new strains of Methylocystis bacteria. Further sequence analysis revealed that ml511 shared only a 94.1% sequence similarity with its counterparts isolated from rice paddy effluents. When compared to already characterized Methylocystis strains，Methylocystis sp.