In this article, a 20 kHz ultrasonic waveguide for nano-surface treatment was designed and manufactured. When designing the system, finite element analysis with ANSYS software was performed to find optimal dimensions of the waveguide, which can raise energy efficiency. Consequently an anti-resonance frequency of an Al waveguide with a piezoelectric actuator was 20 kHz, which predicted the experimentally obtained value of 18 kHz well. For the assessment of the performance, Steel Use Stainless (SUS) 304 and chromium molybdenum steel (SCM) 435 specimens were tested. Cross-sectional microscopies of SUS304 were taken and they showed that the treated thickness was $30{mu}m$. Additionally, hardness tests of SCM435 were done and the hardness before the process was 14.0 Rockwell Hardness-C scale (HRC) and after the process was 20.5 HRC, respectively, which means 46% increase. Considering these results, the developed ultrasonic system is thought to be effective in the nano-surface treatment process.