HAZ CTOD tests have been carried out using two types of CTOD specimen, a through-thickness notched type and a surface notched type, extracted from multipass welds of HT50 steel for offshore structural use. The surface notch tends to sample one HAZ region at the crack tip, whereas the through-thickness notch intersects several regions in the HAZ. However, the surface notched specimen shows complicate fracture behavior especially when a stable crack growth occurs, which makes it difficult to measure the toughness of HAZ-microstructure at the fatigue precrack tip. By contrast, with the through-thickness notched specimen, the fracture toughness of the CGHAZ is evaluated practically because the initiation of cleavage fracture is controlled by the CGHAZ intersected by the crack tip. Critical CTOD of the HAZ-notched CTOD specimen decreases with increasing the total size of the CGHAZ along the crack front, which can be explained in terms of the weakest link effect of the CGHAZ. Bearing this size effect of CGHAZ in mind, the through-thickness notched specimen is more useful for the evaluation of the CGHAZ toughness of welds.