Halloysite nanotubes (HNTs) are natural "green" nanomaterials with tubular structures and have exciting potential applications in many fields. Preparation of homogeneous HNTs remains significant challenges in their fundamental studies and applications. Herein, we provide a method for preparing homogeneous and length controllable HNTs by the combination of ultrasonic treatment and two-step uniform viscosity centrifugation. Raw halloysite bundles have been successfully dispersed and cut by ultrasonic scission. Length controllable HNTs (140-240 nm) can be prepared simply by changing ultrasonic treatment time or ultrasonic power. Short HNTs have been successfully separated from the sonicated suspension of raw HNTs by two-step uniform viscosity centrifugation. Transmission electron microscopy, X-ray diffraction and sequential X-ray fluorescence spectrometer measurements demonstrate that the purified HNTs are homogeneous with much less impurities. This simple, rapid, and effective method can be scaled up for industrial preparation of homogeneous and length controllable HNTs. The purified HNTs can be used as high value-added materials in many industrial fields and used as a carrier for a wide range of active agents, such as drugs, cosmetics, and catalysts. The separation method can be used to separate chemically synthesized nanotubes. In addition, a simple method for quick determination of the concentration of HNTs by UV-Vis spectrophotometer has been developed. (C) 2016 Elsevier B.V. All rights reserved.