Use of elevated electric fields and helium-rich gases has recently enabled differential IMS with resolving power up to R ~ 300. Here we applied that technique to a protein (namely, ubiquitin), achieving R up to ~80 and separating many previously unresolved conformers. While still limited by conformational multiplicity, this resolution is some four times greater than that previously reported using either conventional (drift-tube or traveling-wave) or differential IMS. The capability for fine resolution of protein conformers may open new avenues for proteoform separations in top-down and intact-protein proteomics.