Long fibers of high purity single-walled carbon nanotubes (SWNTs) were directly synthesized macroscopically by the modified arc discharge method. The purity of SWNT in fibers that can be obtained, as high as 80% (volume), was evaluated by scanning electron microscopy, thermogravimetric analysis, and Raman spectroscopy. The diameters of the SWNT fibers we obtained vary from 2 to 200 mum with a predomination of 5-20 mum. The lengths can reach as long as 10 centimeters. It is proposed that promoter FeS is a crucial factor for synthesizing high purity SWNT fibers.