The utilization of Zircaloy for pressurized-water, nuclear-power reactor core structure and cladding applications results in numerous design examples with either sharp edge defects or joints which approximate sharp cracks. For the characterization of fracture toughness, specimens were machined from an ingot of Zircaloy-4 which had been hot rolled to a 1-in. thickness and retained in the mill-annealed condition (i.e., hot rolled at 1550°F, reheated to 1550°F for 15 min after rolling, and air cooled). The basal pole fractions were fL = 0.073, fT = 0.415, and fN = 0.512. The testing for fracture characterization was conducted with IX WOL (wedge opening loading) and 0.4X CT (compact tensile) specimens. Orientation effects introduced by the preferential alignment of the basal planes during rolling have been determined by the subsized CT specimens. Also, the fracture surfaces were studied with a scanning electron microscope and evidence of large local ductility was observed for all specimens including those fractured at -150°F. Small hollow conical projections from the fracture surface are superimposed on larger similarly shaped projections. A model for fracture consistent with the scanning electron microscope (SEM) views is the formation of small isolated spheroidal holes, less than 10% of grain size, then growth and coalescence of the holes to form the larger conical projections of grain size or larger.