Abstract: A customer made capillary spinning equipment was applied to spin regenerated silk fibroin (RSF) fibers from concentrated RSF aqueous solutions in air. The effects of metal ions, pH, molecular weight of RSF and spinning parameters on the spinnability of the spinning dopes and the mechanical properties of the obtained fibers were investigated. As a result, spinning dopes with pH from 5.2 to 6.0 have good spinnability, especially for the dope with pH of 6.0 and Ca2+ concentration of 0.3 mol/L. Under the optimized condition (length-diameter ratio of spinning capillary, 133; takeup speed, 30 mm/s), the obtained fiber has the highest breaking strength of 45.5 MPa.