During the past few decades, soil nailing has been widely used for stabilizing slopes and excavations. The nail-soil interface shear resistance in the passive zone of a slope or excavation is a critical parameter in design. In this paper, an analytical study is proposed to investigate the progressive pullout response of a soil nail. Pullout process is divided into three typical phases: (1) the initial pure elastic phase during which the nail-soil interface follows a linear elastic stress-displacement relationship; (2) the elastic-plastic phase during which a transition point presents dividing the elastic and plastic zones; and (3) the final pure plastic phase. A comparison study between calculations and laboratory test data are presented to examine the effectiveness of the method. In addition, a comprehensive parametric study is performed to assess the effects of several key factors on the pullout resistance of a soil nail. These factors include the length and diameter, length of plastic zone, and the elastic modulus of a soil nail. Main research findings are presented and discussed to gain a better understanding of the progressive interaction between soil and soil nail. © 2012 American Society of Civil Engineers.