Transport properties of a novel GaAs/A1GaAs quantum well wires (QWWs) with Schottky in-plane gates were investigated. The QWW was realized by a combination of a electron beam lithography and the in situ electrochemical technology. Clear quantized conductance in units of 2e 2 /h was observed up to 100 K. Nonlinearities are found in the current-voltage characteristics at a small applied voltage, resulting in conductance deviation from the value of the quantized conductance. From the breakdown voltage of conductance quantization, a subband energy separation is estimated to be 10 meV or higher.