We investigated the etching of NbO_x nanopillars that can be used as an etch mask for the formation of Si nanodot arrays. The Nb films were deposited just before an Al film. NbO_x nanopillar arrays were prepared by anodizing of Al and Nb thin film. Etch mechanism of NbO_x nanopillar arrays were investigated using inductively coupled plasma reactive ion etch system. Etch gas, coil RF power and dc bias to substrate were varied. The feasibility of using NbO_x nanopillars as an etch mask was examined by exploring the etch mechanism of NbO_xnanopillars.