Polycarbosilane particles were dispersed in a novolac-phenolic resin matrix, and the resulting polymer blend was meltspun, stabilized and heat-treated at 1000°C or 1200°C for 1 h in an inert atmosphere. The heat-treated blend fibers were oxidized in nitric acid solution to remove the carbon matrix and the nanofibers thus released were collected by filtration. The nanofibers obtained from the 1000°C-blend fibers were oxidized more severely by nitric acid, resulting in a rougher nanofiber surface compared with that of nanofibers from the 1200°C-blend fibers. The former nanofibers also showed a larger specific surface area (288 m²/g) than did the latter (44m²/g). Analysis of a filament from the 1200°C-nanofibers showed carbon present at about 30 atom %, whereas just a few atom % of carbon was found in the 1000°C-nanofiber. It was concluded that more intact nanofibers with stronger oxidation resistance were derived from the polymer blend fibers heated at a higher temperature.