In this paper, we investigate the relationships between stick-slip defect and molecular slip at the wall for linear polymers. By considering Brochard-de Gennes slip model and molecular chain dynamics at the wall, we propose expressions for the critical shear stress and the critical shear rate at the onset of stick-slip. Moreover, we present a criterion of existence for the stick-slip defect, based on the molecular weight distribution. These various expressions are qualitatively validated by experimental data from the literature. (C) 2009 Elsevier B.V. All rights reserved.