A two-step sharpening process for a Si pillar in a quartz tuning fork sensor was developed for use in frequency modulation atomic force microscopy (FM-AFM). By combining electrochemical etching in HF solution and anisotropic etching in KOH solution, the tip radius was decreased to 120 nm. The Si-probe-attached sensor showed a higher resonance frequency than a tungsten-probe attached sensor, which would lead to a higher force sensitivity. We demonstrated FM-AFM imaging on a cleaved mica surface in aqueous solution by using the fabricated sensor, and atomic resolution was successfully achieved.