Reproducible high-yield purification process of singlewalled carbon nanotubes was developed by combining two-step processes of thermal annealing in air and acid treatment. The process involves the thermal annealing in air with the powders rotated at temperatures of 470 degreesC for 50 min, which bums out the carbonaceous particles, and an acid treatment with HCl for 24 h, which etches away the catalytic metals. Control of the annealing temperature and rotation of the sample are crucial for high yield. Our reproducible optimal purification process provides a total yield of about 25 similar to 30 wt % with less than 1 wt % of transition metals, which was confirmed by the thermogravimetric analysis. Bundling and length control depending on the different acid treatments will be further discussed.