The present invention is directed to a polyacetal stretched fiber of a polyacetal resin composition which contains a polyacetal resin and a fatty acid metal salt in an amount of 0.01 to 5 phr relative to the polyacetal resin, wherein the stretched fiber is obtained by stretching a fiber at a temperature of 100° C. or more to a temperature lower than the melting point of a polyacetal resin composition, and the fiber is obtained by melt spinning the polyacetal resin composition, and a fiber assembly comprising the stretched fiber as a main constituent.