A solid phase preconcentra- tion method has been developed using hydroxyl multi-wall carbon nanotubes (MWNTs) as the absorbent. The method was opti- mized for the determination of rare earth elements (REEs) in deep groundwater samples by inductively coupled plasma mass spectrometry (ICP-MS). The effects of the experimental para- meters, including pH, eluent con- centration and volume, flow rates of sample and eluent solutions, and the sample volume on the recoveries of the analytes were examined in detail. Under opti- mum conditions, REEs can be quantitatively retained by MWNTs when the pH exceeds 3.0 and are then eluted com- pletely with 1% HNO3. The detection limits of this method ranged from 0.31 ng L-1 to 1.2 ng L-1 and the relative standard devi- ations (RSDs) were less than 5%. The method was validated using a certified reference material and was applied for the determina- tion of REEs in deep groundwater samples with satisfactory results.