Recently,‘Candidatus Methylomirabilis oxyfera (M. oxyfera)’ belonging to the candidate phylum NC10 was investigated in incubated culture or freshwater sediments. NC10 couples “denitrification” with generating oxygen from nitrite to oxidize CH ₄under anoxic environment. In the present study, the patterns of NC10 and other MOB were examined from Oct 2012 to Feb 2014 in subtropical reservoir (Fei-tsui Reservoir; FTR), in Taiwan. Catalyzed reporter deposition- fluorescence in situ hybridization (CARD-FISH) was used to demonstrate the abundance of NC10 with other MOB groups (type I and type II). CARD-FISH analysis revealed that all MOB types were detected during the observation period. The number of NC10 dominated at close to the oxic–anoxic interface and detected 2.5 × 10⁵ cells ml^-1 at near the bottom in the presence of methane (18.3M) after winter vertical mixing in Feb 2013. On the other hand, type II was dominated at upper layers with low methane concentration and type I were observed through the water column. These results suggest that NC10 was significant MOB members especially under the reduced condition (low DO and nitrate concentrations) and may play an important role to consume CH₄ in this subtropical reservoir.