Abstract: New materials have significant impact on development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes (SWCNTs and MWCNTs) -due to their high adsorption and desorption capacities- have been employed as sorption substrates in solid-phase extraction for the preconcentration of heavy metals from diverse matrices. In the present work, a new method for the Pb determination by electrothermal atomic absorption spectrometry (ETAAS) in urine at low levels has been developed. Lead was separated from the undesirable urine matrix by means of a solid phase extraction (SPE) procedure using oxidized multiwalled carbon nanotubes as a sorbent material.