Creep deformation of cast nickel base superalloy 713LC has been investigated in a temperature range of 723 to $982^{circ}C$. The values of the stress exponent and activation energy for creep of the alloy vary with a combination of temperature and stress. Introduction of threshold stress for creep of the alloy provided an explanation of the high values of the stress exponent and the apparent activation energy. Microstructural evolution of the alloy with creep deformation has also been studied. The analysis of the creep mechanism has been supplemented by microstructural observations after deformation under various test conditions. The dislocation structure of the alloy at high temperature and low stress was different from that at low temperature and high stress. Shearing of $gamma'$ particles by dislocation pairs was the dominant creep mechanism at low temperature and high stress whereas dislocation climb over $gamma'$ particles was the rate controlling process of creep at high temperature and low stress.