As-spun filament of copolyacrylonitrile(AN/MA=95/5w1%) has been prepared and subsequcntly stretched. The stretched filaments which contain moisture were shrunk freely by 5%~25% on heating in dry air at 130~17$0^{circ}C$. The change of morphology and mechanical properties was examined by various techniques such as thermal mechanical analyzer(TMA), scanning electron microscopy(SEM). rheovibron and tension. After heat treatment, residual shrinkage of fiber decreased significantly with increasing shrinkage, while it was little affected by heat treatment temperature. Electron microscopy revealed that surfaces of acrylic fibers were grooved along the fiber axis. The grooves developed by the collapse of voids during the process of drying increased slightly with increasing shrinkage and heat treatment temperature. Maximum tan § peak became broader with increasing shrinkage. Consequently, enhancement in thermal dimensional stability and mechanical properties of fibers treated under these conditions(16$0^{circ}C$$ imes$10%) may be due to an optimum increase of dipole bonds between -CN groups.