Iodine-Induced Stress Corrosion Cracking (ISCC) properties of Zircaloy-4 and HANA4 developed in KAERI for the high burn-up nuclear fuel cladding were evaluated. To confirm the effect of final heat treatment on ISCC resistance of Zr-alloy, stress relieved and recrystallized specimens were prepared and tested. With the pre-cracked specimen at internal surface, ISCC crack propagation rates and threshold stress intensity factor ($K_{ISCC}$) based on the fracture mechanics were measured by internal pressurization test at $350^{circ}C$ in iodine environment. $K_{ISCC}$ of Zircaloy-4 and HANA4 cladding were $3.3MPa{cdot}m^{1/2}$ and $4.4MPa{cdot}m^{1/2}$, respectively. Pitting corrosion at the crack surface was observed and it seemed that TG crack propagation was derived from the pitting.