Failure analyses of weld joint between the nozzle and the head of the reactor made of 2205 duplex stainless steel was performed by optical microscopy (OM) and scanning electron microscopy (SEM). Cracks were found in HAZ of the weld. The depth of the cracks is equal to the thickness of the inner weld. Localized uneven distribution of ferrite/austenite with 80-90% ferrite in weld is found. Results show that the cracks occurred along columnar granular with cleavage fracture. Poor weld process probably results in these cracks.