PURPOSE: To obtain the titled fibers having sufficient heat resistance and flame retardancy, excellent mechanical strength as well as solvent resistance and useful as reinforcing fibers, etc., by melt spinning a polycyanoaryl ether, consisting of specific repeating units and having a reduced viscosity within a specific range.

CONSTITUTION: A polycyanoaryl ether, containing ≥80mol% repeating units expressed by the formula and having 0.5W3.0dl/g [ηSP/c] (measured by a 0.2g/dl p-chlorophenol solution at 60°C) is melt spun, preferably at 345W360°C. The resultant fibers are then drawn, preferably at 150W180°C temperature at ≥1.5 draw ratio to afford the aimed fibers.