This study reports the development of an amperometric biosensor for quantification of mevalonic acid (MA), which is the first intermediate of HMG-CoA reductase in the isoprenoids biosynthesis pathway and therefore a useful indicator of HMGR activity. This method offers important advantages over previous reports because no radiolabeled substrates or expensive techniques are required, and time of analysis is relatively short. Self-assembled NAD(+) onto multiwall-carbon nanotubes (MWCNTs) was synthesized for a biosensing system. Adsorption of NAD(+) on MCWNTs was characterized by X-ray photoelectron spectroscopy (XPS) technique. This biosensor was constructed by modifying a screen-printed carbon electrode (SPCE) with NAD(+)/MWCNTs nanocomposite. The electrochemical and electrocatalytic behaviors of the modified electrode were studied using amperometry and cyclic voltammetry (CV). The resulting biosensor demonstrated great electrocatalytic activity, good stability and fast response to MA. At the NAD(+)/MWCNTs-modified SPCE, the catalytic currents are linearly proportional to the concentrations of MA in the wide range from 10 nM to 140 nM with a limit of detection down to 5 nM (S/N = 3), and the biosensor exhibited a sensitivity of 18.3 mu A/mM. We measured the interference effect on the MA analysis and the results demonstrated its imperviousness to the effects of haemoglobin, bilirubin and serum albumin. (C) The Author(s) 2017. Published by ECS. All rights reserved.