We focus on nanoscale copper-rich precipitates and try to clarify the effect of the nanoscale copper-rich precipitates on embrittlement of reactor pressure vessel steels. Our final goal is to evaluate such embrittlement from microscopic viewpoint based on atomistic simulation. In this study, we simulate interaction between motion of an edge dislocation and copper precipitates using Molecular Dynamics (MD) method with a periodic boundary condition, where uniform shear strain is applied to the boundaries parallel to the slip plane (112) in the system. Comparing motions of the edge dislocation among models with copper precipitates in different diameter, it is found that the larger the copper precipitates are, the more decelerated the motion of the edge dislocation is by copper precipitates.