Mechanical behaviors of metallic materials in a small scale are characterized and physically modeled based on experimental measurements and computational simulation. Local
plasticity in the vicinity of a grain boundary is considered in terms of an interaction between dislocation and grain boundary. It is shown experimentally that nanoindentation technique can
detect a resistance to dislocation slip transfer by a grain boundary with a geometrical or a chemical factor. Molecular dynamic simulation revealed that the geometrical effect depends on not
only a misorientation but also a combination with a dislocation character. TEM in–situ straining has a great potential to measure directly a critical stress upon slip transfer as well as a
dislocation reaction at a grain boundary. Another potential reaction of a dislocation absorption at a grain boundary was discussed based on both the experimental results by TEM in–situ
observation and the atomistic simulation in bcc metals.