In this study, we investigated the effects of different mastication on dispersion of carbon black (CB) and mixing using NBR with different raw material rubber viscosity and acrylonitrile content. In addition, the effects of rheological unit on the order of ƒÊm, which are considered to be caused by mastication, on them were discussed. In NBR, CB dispersion is improved by sufficient mastication and mastication at low temperature. Furthermore, CB is easily dispersed in the case of NBR with low viscosity or high acrylonitrile content. On a microscopic scale, if CB incorporation is completed with large rheological unit remaining due to insufficient mastication, these large rheological unit remain until the end of mixing, which contributes to CB dispersion reduction. We found that the subdivision of NBR on the micro-scale has a greater effect on CB dispersion than the viscoelasticity of masticated NBR on the macro-scale. On the other hand, for BIT, temperature of masticated NBR on the macro-scale has a greater effect than the subdivision of NBR on the micro-scale.