Dislocation structures of Fe-35%Ni invar alloy single crystals deformed at room temperature have been observed by transmission electron microscopy. The peculiar characteristics of dislocation structures are as follows : 1) most of the residual dislocations after plastic deformation are cusped screw ones in the early stage of deformation and increase in edge components with increasing strain, 2) dislocation loops exist with high density, distributed homogeneously and form weak obstacles against other dislocation motion, 3) a dislocation accumulation is observed, but does not tangle heavily. It is shown that these experimental results can be explained by the invar properties of these alloys
