Controlling microdomain structure of block copolymers (BCPs) under electric field has been one of the most challenging research tasks. In this study, we examined the effect of nanoparticles on the microdomain orientations in BCP/nanoparticle thin films under electric field using cross-sectional transmission electron microscopy experiments. Gold and cadmium selenide nanoparticles with a tailored surface property were incorporated to control microdomain orientations in BCP/nanoparticle thin films by varying dielectric constant of one constituting block. It was revealed that the microdomain orientation of BCP/nanoparticle thin films under electric field was suppressed by the introduction of gold nanoparticles. Thus, it can be inferred that gold nanoparticles can show a shielding effect under external electric field. The effect of complementary parameters such as NPs concentration, exposure time, and field strength were also demonstrated. In addition, it was also found that the suppression effect lessened with cadmium selenide nanoparticles having a dipole from the noncentrosymmetric structure. This work can provide fundamental data for understanding of microdomain alignment behavior of BCP/nanoparticle system under electric field.