Simultaneous determination of ascorbic acid (AA) and caffeine (CAF) in pharmaceutical preparation is important and it has been achieved by square wave voltammetry (SWV) using a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT). The oxidation of M and CAF at MWCNT occurred at similar to-10 mV and similar to 1103 mV at a much lower potential, than that observed (similar to 202 my and similar to 1402 mV) for their oxidation at bare GCE. The mechanistic study has shown that the equal number of electrons and protons are involved in the oxidation of drugs. The electrodes could be used for the determination of AA and CAF in a wide concentration range 10-500 mu M, respectively, whereas the detection limit has been found to be 1.0 x 10(-2) mu M and 3.52 x 10(-3) mu M respectively. In view of high sensitivity for the detection of the drugs, the technique has been used for the reliable determination of AA and CAF in tea leaves, coffee, cold drink (mountain dew), pharmaceutical preparations and urine samples. (C) 2013 Elsevier Ltd. All rights reserved.