Testing conditions of the double loop electrochemical potentiokinetic reactivation(EPR) test have been modified to obtain the most optimum condition in detecting the sensitivity to intergranular attack(IGA) for Alloy 600 and the degrees of sensitivity to IGA measured by the modified EPR test have been compared with those to IGSCC for Inconel 600 to determine the relation between these. The Inconel 600 samples have been sensitized for 1 to 100 hours at 700℃ and the effects of sensitization time on the degree of sensitivity to IGA has been evaluated by the ratio of $I_r$(the maximum current density at reverse scan) to $I_a$(the maximum current density at anodic scan) in the double loop test with varying solution concentration, temperature and scan rate. The most optimum testing condition was obtained in 0.01M $H_2SO_4$ + 0.0001M KSCN at 25℃ and at scan rate of 0.5mV/sec in which the Cr-depleted zone was clearly observed and the ratio of $I_r$/$I_a$ exhibited substantially different values depending on sensitization time. For the sensitized Alloy 600 samples except those sensitized for less than 1 hour, the degrees of sensitivity to those to IGA measured by the modified EPR test parallel to IGA revealed by the ratio of strain to failure ($\epsilon_{f,Na2S406}/\epsilon_{f,air}$) measured in 0.01M $Na_2S_4O_6$ solution using CERT tester. IGSCC occurs in samples sensitized shorter than 10 hours at 700℃ and the degree of sensitivity to IGSCC increases with decreasing sensitization time. It was demonstrated that the degree of sensitivity to IGSCC is closely associated with both the width of Cr-depleted zone and the depth in the Cr-depleted concentration profile across grain boundary.