In this letter, single-walled carbon nanotubes (SWCNT) coating was used on the D-shaped silica fiber for ethanol sensing in aqueous solution. The performance of this structure as an ethanol sensor was studied here by monitoring output power variation and wavelength shift with changing ethanol concentration. In the concentration range of 5%—50% of ethanol, the SWCNT coated structure showed an improved sensitivity compared to the uncoated sample. The sensitivity is improved from 0.013 5 dB/% to 0.040 9 dB/% with the coating. The SWCNT coated sample also showed a peak wavelength shift of 0.1 nm with the change of ethanol concentration in the same range.