Initially, we investigated the catalytic NaNO2/acid system for the aerobic oxidation of methane under ambient conditions, which was used successfully in our aerobic bromination of alkanes under visible-light at room temperature before. In the presence of 2.4 mol% NaNO2 based on CH4 in HCl (12 M) solution, only a trace of CH3OH and methyl nitrate (CH3ONO2) were detected by 1 H NMR analysis in the reaction of CH4/O2 (2:1, 0.1 MPa) under irradiation by 23 W LED at 298 K after 24 hours. It seems that the oxidation of methane did not proceed very well since the catalytic NaNO2 was fixed in CH3ONO2 to stop the reaction. Then, HTFA was added into the solution to transfer CH3ONO2 to MTFA and HNO3 under the same conditions. Of course, no CH3ONO2 was detected, and methyl chlorides CH3Cl/CH2Cl2 were the major products (92% selectivity) in 39.7% yield based on methane. Notably, MTFA in 2.7% yield and HCO2H in 0.8% yield were also found in the products. In contrast, when NaNO2 loading was reduced to 0.024 mol%, only MTFA was produced in 2.7% yield without any other products and the TON was over 100 in 24 hours. It implies that the amount of NaNO2 could affect the selectivity of MTFA seriously, and the modified catalytic system of NaNO2/HCl/HTFA should be effective to the conversion of methane to MTFA in an aerobic oxidation of methane under ambient conditions. Just by use of 0.24 mol% NaNO2 (2.3 μmol) in HCl (12 M, 0.18 mL)/HTFA (0.7 mL) solution, it was found that MTFA could be produced as the major product in 15.7% yield from CH4/O2 (2:1, 0.95 mmol/0.48 mmol, 35 mL, 0.1 MPa) under 23 W LED at 25 o C after 24 hours. The selectivity of MTFA was 91% just with a small amount of CH3Cl (5%) and HCO2H (4%). No other byproducts including formaldehyde, nitromethane and carbon dioxide were detected by H NMR and IR analysis. The turnover frequency (TOF) was 2.8 mol MTFA mol NaNO 2 -1 h -1 in this batch experiment. The performance of sodium nitrate NaNO3 was not different from NaNO2 in the aerobic oxidation (Figure , Table ). However, if HCl was replaced by hydrobromic acid HBr or in the absence of HTFA, O2 or light, no methyl ester was detected. In the cases of using 2.3 μmol NaNO2 under normal pressure in the same reactor (Table ), we also found that air was available to give MTFA in 92% selectivity and CH3Cl, and the TOF was 2.1 mol MTFA mol NaNO 2 -1 h -1 . If the ratio of CH4/O2 was up to 24:1, O2 could be consumed almost completely in 24 hours. The yields of MTFA and CH3Cl based on O2 were 70.7% and 23.6% respectively. On the other hand, when the ratio of CH4/O2 was down to 1:5, HCO2H as the major product and MTFA (~3:1) were formed in total 24% yield, and no methyl chlorides were found (Figure ). These results shows that the formation of byproducts was related to the ratio of CH4/O2, i.e., methyl chlorides were generated easily in the lack of O2, but HCO2H was formed quickly in the rich of O2.