The effects of spinning conditions on the filament irregularity and the periodicity of irregularity caused by draw resonance in the melt spinning of polypropylene were investigated. The filament irregularity increased with the increase of draw ratio at both isothermal and nonisothermal conditions, but the slope of irregularity versus draw ratio and the period al nonisothermal conditions were smaller than those at isothermal condition. In both isothermal and nonisothermal conditions, the filament irregularity increased with the flow rate, but decreased with spinning temperature. In the isothermal conditions, filament irregularity increased with the spin length, but decreased in nonisothermal condition. When the draw ratio was increased, the amplitude of the fiber diameter variation increased, but the frequency of oscillation was unchanged. This results illustrated that the draw resonance is a hydrodynamic instability The period of irregularity caused by draw resonance increased with spin length, and decreased with flow rate, but spinning temperature had no effect on the period.