PURPOSE: To rationally produce a large-sized parent material providing a single mode optical fiber capable of securing low-loss properties, in production of the parent material for the single mode optical fiber showing a variance within a range of ±10ps/km/nm2 in a wavelength within a range of 1.27μm-1.57μm.

CONSTITUTION: In the specified invention method, a quartz-based glass rod (glass for core and glass for part of clad) is produced by MCVD method and glass for the remainder quartz-based clad is produced on the outer peripheral surface of the above-mentioned glass rod by VAD method and/or OVD method. In a related invention method, the glass rod produced by MCVD method is subjected to etching treatment and glass for the remainder quartz-based clad is subsequently produced by VAD method and/or OVD method. The specified invention method enables high yield, scaling up and high productivity of the product and the related invention method enables, in addition to those, production of a parent material capable of forming a single mode low-loss optical fiber.