In order to demonstrate silica nanomachining, the authors fabricated line-and-space contact masks with spaces of 53 and 70nm on silica glass plates, followed by irradiation with laser plasma softx rays (LPSXs) with wavelengths around 10nm. Trenches with the narrowest width of 54nm and an aspect ratio of ∼1 were fabricated by the LPSX irradiation through the contact masks. It was also clarified that silica glass can be machined by irradiation with LPSXs in the wavelength range of 6–30nm in Ar gas which was used as an x-ray bandpass filter.