Hydrogen-induced cracking (HIC) of two-phase alloy of Ni3Al+NiAl was in situ investigated using a WOL (wedgeopening-loading) constant deflection specimen in an optical microscopy and using a notched tensile specimen in scan-ning electron microscopy (SEM). Results showed that the threshold stress intensity of HIC was KIH=15.7 MPa.m1/2,and (da/dt)Ⅱ=0.019 mm/h. For the uncharged specimen, microcrack initiated and propagated preferentially withinthe NiAl phase, resulting in cleavage fracture, but for the precharged specimen with hydrogen concentration of24.7× 10-4%, hydrogen-induced crack initiated and propagated preferentially along the Ni3Al/NiAl interfaces, result-ing in interphase fracture.