In this article, the effects of fundamental parameters including applied voltage, feed rate of solution, collecting distance of fibers, the ratio of chitosan to collagen in the fibers and polymer solution concentration on the diameter and morphology of electrospun collagen-chitosan complex nanofibers were studied to produce ultrafine polymer fibers. Based on the systematic parametric study, it is possible to control the diameter and morphology of the electrospun polymer fibers. This will also be helpful for electrospinning of various polymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1949-1955, 2009