An object of the present invention is to provide: a process for conveniently producing a fiber with high strength, regardless of molecular weight polymer composition, or the like of PHAs, which vary depending on origins such as a wild-type PHAs-producing microorganism product, a genetically modified strain product, and a chemical product; and the fiber with high strength produced through the process.The present invention provides: a process for producing a fiber, comprising: melt-extruding polyhydroxyalkanoic acid to form a melt-extruded fiber; rapidly quenching the melt-extruded fiber to the glass transition temperature of polyhydroxyalkanoic acid +15° C. or less, and solidifying the fiber to form an amorphous fiber; forming a crystalline fiber by leaving the amorphous fiber to stand at the glass transition temperature +15° C. or less; drawing the crystalline fiber; and further subjecting the crystalline fiber to stretch heat treatment.