The jet stretch of dry-jet wet spun PAN fiber and its effects on the cross-section shape of fibers were investigated for a PAN-DMSO-H2O system. Clearly, the spinning parameters, such as dope temperature, bath concentration, bath temperature, and air gap, all influenced the jet stretch. Also, under uniform conditions, the postdrawing ratio as well as that of jet stretch changed. Under given conditions, as the bath temperature was below 30 degrees C or above 45 degrees C, jet stretch had little effect on the cross-sectional shapes of PAN fiber. Within the temperature of 30-45 degrees C, fiber's cross-section shapes change obviously from round over an approximate circular shape into to an elliptical or a flat shape. The scope of jet stretch produced PAN fiber with circular cross-section was bigger than that in wet spinning. These results indicated that appropriate air gap height, under milder formation conditions in dry-jet wet spinning, could result in higher jet stretch and higher postdrawing ratio. The appropriate jet stretch and postdrawing ratio could result in circular profile of PAN fiber, which were helpful to produce round PAN precursor with finer size and better properties for carbon fiber. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:3621-3625, 2009