Polyamide 6 (PA 6) filaments with initial modulus around 48 GPa were produced by dry spinning from low mole ratio (MR) complex of calcium chloride and high molecular weight PA 6 (CaCl2-PA 6) in formic acid. From the results of XRD, DSC, FTIR, and SEM, the complexation of CaCl2-PA 6 in the MR range of 0.15-0.3 was efficient. The spinnability of the complex solution was excellent, which allowed a maximum draw ratio of 14.4 for as-spun fibers. After decomplexing and annealing, the birefringence of drawn fiber could reach around 0.08. Porous structure was found in fibers spun from formic acid-chloroform cosolvent but not observed by using pure formic acid. When MR of CaCl2/PA 6 exceeded 0.3, some irregular particles formed on the fiber surface due to the recrystallization of CaCl2. However, fibers with smooth surface could be obtained when the MR decreased to 0.15. During the process of decomplexing in ethyl alcohol, an axial shrinkage of drawn fibers in a relaxed state was observed. It turned out that this shrinkage could be avoided by decompexing the fibers under tension. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 1996-2004, 2010