In this study, we proposed an electro-rheological fluid-aided polisher (ERAP) using one-sided, patterned electrodes. The characteristics of ER fluid and ER fluid containing abrasive grit were investigated. The polishing performances of ER fluids with and without abrasive grit employing ERAP were verified and the following conclusions were obtained. Decreases in viscosity and in the ER effect were observed when highly polymerized liquid crystal (hereafter referred to as HPLC) was diluted with silicon oil. However, the mixing of abrasive grit increases the ER effect, but the ER effect of ER fluid containing abrasive grit decreased when mixed with abrasive grit. The viscosity decreased with increases in aliphatic saturated cyclic hydrocarbon oil (hereafter referred to as NCDM) mixed in highly polymerized compound (one kind of HPLC). The larger the positive dielectric anisotropy, the larger the ER effect in low-polymerized liquid crystal (hereafter referred to as LPLC). The smaller the grit size, the weaker the ER effect. When polished with HPLC, the polished surface was rough due to the large viscosity of an HPLC:silicon oil ratio of 4:14 mixed with #2000WA. However, the smallest surface roughness was attained at 0.5kV/mm for an HPLC:silicon oil ratio of 1:17 mixed with #2000WA. The surface quality was improved at an HPLC: silicon oil ratio of 1:17 mixed with #3000WA. When polished with LPLC, the surface roughness was improved by the increased ER effect when LPLC having a positive dielectric anisotropy was used. However, the surface roughness showed no change when LPLC with a negative dielectric anisotropy was used, due to its small ER effect.