Experimental studies on the density and moisture regain of nylon 6 fibers with varying draw ratios and draw temperatures have been carried out. Relationships among fiber densities, moisture regains, draw temperatures and draw ratios, and various combinations of these properties are analyzed. Results from these analyses are as follows: 1) The density of nylon 6 fibers increases with the moisture regain at the early stage of absorption and decreases after a certain value. 2) fiber density increases rapidly with the increase of draw ratio up to about 2 and after it increasing rate becomes small. 3) As the draw ratios and draw tempertures become higher, peak points of the curves of moisture regains and densities move toward the higher density and the lower regains. 4) the structure of nylon 6 fiber is unstable at draw ratios between 1∼2. 5) Mechanisms of change of the structure and mechanical properties of nylon 6 fibers due to drawing and temperature are different.