Unique SnO2 monoflowers with an aloe-like morphology were successfully synthesized via a one-step hydrothermal method. The structural, chemical, and physical characteristics were investigated. The results exhibited that the as-prepared sample was assembled by triangle rutile SnO2 nanoslices with rough surfaces. A possible crystal growth and nanostructure assembling mechanism was proposed. The Raman peaks in 171, 235, and 211 cm−1 proved that a large amount of oxygen defects existed inside the sample, which might narrow the band gap from 3.6 eV of pure SnO2 to 2.7 eV of the sample. The sensor fabricated by aloe-like SnO2 nanostructures exhibited an excellent response and selectivity to ethanol. The developed sensor can detect ethanol as low as 10 ppm at 360 °C. The prepared aloe-like SnO2 microflower sensor exhibited a gas sensing response of about 7.46 when exposed to 100 ppm of ethanol gas at 360 °C, which was probably related to more numerous defects and thinner structure of aloe-like SnO2.