Poly(1-oxotrimethylene) (ECO) was dissolved in an aqueous composite metal salt Solution, and the ECO solution was heated at different temperatures and then used for wet spinning. Within a certain heating time, ECO fibers with a tenacity of 17.6 cN/dtex (2.3 GPa) or greater were successfully produced through hot drawing 16-17 times after drying. Over a certain heating time, however, the strength of the ECO fibers drastically decreased. A higher heating temperature shortened the heating time at which the drastic decrease in the maximum tenacity began. On the basis of ultraviolet measurements of the undrawn fibers, heating ECO in the aqueous composite metal salt solution promoted the thermal degradation of ECO because of aldol condensation or Paal-Knorr furan synthesis. The thermal degradation due to these intermolecular or intramolecular crosslinking reactions was resistant to the molecular orientation of ECO by the hot drawing of the undrawn fibers and reduced the strength of the ECO fibers by producing defects in the filament. (c) 2006 Wiley Periodicals, Inc.