A novel carbon monoxide (CO) sensor is fabricated based on quartz crystal microbalance (QCM) using commercial piezoelectric crystal, modified with single-walled carbon nanotubes (SWCNTs) through spin-coating technique. For this purpose, a 10.00 +/- 0.03-V alternative-current (AC) potential with frequency of 4.62 +/- 0.02 MHz as an optimum surface acoustic wave (SAW) is applied to the piezoelectric crystal (SAW device). To follow the linear correlation between mass difference and frequency gradient, a frequency-to-voltage converter is adopted using an integrated circuit. Output potential is then filtered by electrical high-pass filter, followed by 10 fold samplification using an operational amplifier and finally connection to a PC through a voltmeter. According to figures of merit, fabricated sensor is linear from 35 to 280 parts per million (ppm). Detection limit is also similar to 5.3 ppm. Relative standard deviation for six replicate analyses is 3.04%. Based on 90% of maximum response (t(90)), response time is 5.0 s. Recovery time is also evaluated to similar to 30 s at 1.0 atmosphere pressure. Calibration sensitivity is measured to 0.057 mV/ppm. No significant interference is observed, when introducing at least 500 folds of various foreign species in air as diluents. Reliability of the sensor is finally evaluated via determination of the CO in two samples.