Pristine activated carbon (AcC) was oxidized by H2O2 under ultrasonic conditions. Compared with pristine AcC, the H2O2-oxidized AC possesses higher accumulation ability to trace levels of Cd2+. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd2+. In 0.01 mol L-1 HClO4 solution, Cd2+ was effectively accumulated at the surface of H2O2-oxidized AcC modified paste electrode, and then reduced to Cd under - 1.10 V. During the following potential sweep from - 1.10 to - 0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at - 0.77 V. The stripping peak current of Cd2+ changes linearly with concentration over the range 5.0 x 10(-8) to 5.0 x 10(-6) mol L-1. The limit of detection was found to be 3.0 x 10(-8) mol L-1 for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd2+ in waste water samples.