Proteins were separated using a cross-axis coil planet centrifuge equipped with two different types of coiled columns, i.e., toroidal and eccentric coil assemblies. An aqueous-aqueous polymer phase system composed of 12.5% (w/w) polyethylene glycol 1000 and 12.5% (w/w) dibasic potassium phosphate was used for the separation of cytochrome C, myoglobin and ovalbumin. The toroidal coil assemblies with 1 mm ID tubing yielded the partition efficiency of 170 theoretical plates at the myoglobin peak. A slightly higher efficiency was obtained from the eccentric coil assemblies with the same diameter. The highest partition efficiency of 450 theoretical plates was attained from the eccentric coil assemblies with 0.85 mm ID and 64 mL capacity.