Polyglycolic acid (PGA) is an aliphatic polyester with the simplest chemical structure. PGA has biocompatibility and biodegradability. Therefore, it has been applied for surgical suture. One of the disadvantages of the PGA, however, is a narrow window of processing conditions, which makes it difficult to produce high-strength fibers. In general, fibers of good mechanical properties are produced through the drawing of as-spun fibers of low molecular orientation. For PGA fibers, even though the take-up velocity was kept at a low level, maximum draw ratio of the as-spun fibers and achievable mechanical properties were limited. In a previous study of developing high-strength poly(ethylene terephthalate) fibers, we introduced the concept of "melt structure control". Control of the state of molecular entanglement is the more concrete description for the melt structure control, which might be accomplished through the change of the flow behavior of polymer melt in the melt spinning process. Based on the concept stated above, a heating chamber was installed in the vicinity of a spinning head to reduce the Deborah number during the thinning of the spin-line. As the result, toughness of the as-spun PGA fibers was improved successfully. After the application of continuous drawing process to the as-spun fibers, the drawn fibers of high-strength and high toughness could be prepared. To verify the concept of controlling the state of molecular entanglement, we analyzed the network draw ratio and entanglement density of the as-spun fibers through the super-position of the true stress vs. true strain curves and the measurement of heat shrinkage stress. The entanglement density in the as-spun fibers was found to increase by installing a heating chamber. It was speculated that the formation of highly homogeneous state of molecular entanglement resulted in the improvement of the essential mechanical characteristics of the PGA fibers.