Characteristics of subcritical cracking(SCC) in HY-steels were studied focussing on the effect of yield strength on SCC property. In order to accelerate the SCC phenomena and thus to shorten the test period, a new SCC test procedure, so called step-loading SCC test, was developed employing single-edge notched(SEN) tensile specimens. Applying this test procedure on the specimens having six different strength levels, it could be demonstrated that HY-steels having a yield strength over 111㎏/㎟(158 ksi) were highly susceptible to SCC but those having a yield strength lower than 83㎏/㎟(118 ksi) were substantially resistant to SCC. Such an improvement in SCC resistant with lower yield strength was accompanied with the change in failure mode from either quasi-cleavage or intergranular to micro-void coalescence fracture.