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The deformation behavior of (1 1 1), (1 1 0) and (0 0 1) oriented Ni3Al single crystals was investigated by means of nanoindentation. Upon loading with the blunt and sharp indenter tips, the crystal deforms elastically in the initial stage followed by plastic deformation of which the onset is characterized by an obvious displacement burst (or pop-in) in the loading curve. This pop-in corresponds to homogeneous nucleation of dislocation loops under the indenter. When a sharp indenter tip was used, a major pop-in can be identified at a large load (∼7 mN for (1 1 1) crystal) in the plastic regime on loading. The major pop-in may be correlated with the special dislocation structure of the K–W locks in the Ni3Al crystals that are formed during loading. The pop-in behavior during plastic deformation of Ni3Al crystals is found to be closely related to the crystal orientation, pre-existing dislocation density in the sample surface, loading rate, and holding (at a constant sub-critical load) time as well. Pop-ins were also observed at critical loads in unloading processes. [Copyright &y& Elsevier]