In this paper, a two-step AC electrochemical etching process was investigated for the fabrication of platinum probes with controllable aspect ratio from 10 to 30, and tip apex radius less than 300 nm. Experiment results show that the shape of the obtained probes is quite sensitive to the etching time of the first step and the voltage applied in the second step. A graphite crucible was used as the counter electrode during etching. It is proved that the shape of the counter electrode also play a key role for realizing high-aspect-ratio probes. The method presented here provides a simple way in the fabrication of micro-tool for the construction of high-aspect-ratio microstructures, especially for the 3D electrochemical micromachining.