In this paper, a graphene (GR) and double-stranded DNA (dsDNA) composite material was prepared and used for the immobilization of horseradish peroxidase (HRP) on the surface of a carbon ionic liquid electrode (CILE). Direct electrochemistry and bioelectrocatalysis of HRP incorporated in the composite film were carefully investigated. The presence of the dsDNA-GR biocomposite film on the electrode surface could provide a specific microenvironment for HRP with its direct electron transfer rate greatly enhanced on the electrode, which could be attributed to the synergistic contributions of the materials used. Cyclic voltammetric results exhibited that a pair of well-defined quasi-reversible redox peaks was observed on Nafion/HRP-dsDNA-GR/CILE in 0.1 mol/L pH 3.0 phosphate buffer solution with the formal potential (E-0) as -0.193 V (vs. SCE), which was the typical characteristics of the heme Fe(III)/Fe(II) redox couple. The electrochemical parameters, such as the electron transfer coefficient (alpha) and the electron transfer rate constant (k(s)) of HRP in the dsDNA-GR composite modified electrode were calculated with the results as 0.46 and 0.495 s(-1), respectively. The fabricated HRP modified electrode showed excellent electrocatalytic activity to the reduction of trichloroacetic acid over the concentration range of 1.0-21.0 mmol/L with the detection limit of 0.133 mmol/L (3 sigma). So the modified electrode provided a potential platform for the third-generation electrochemical biosensor. (C) 2012 Published by Elsevier Ltd.