Magnetization reversal by electric field has recently been confirmed in cobalt-substituted bismuth ferrite (BiFe_0.9Co_0.1O₃) thin films, which would be applicable to ultra-low energy consumption memory devices. In this study, we fabricated the nanodot array using pulsed laser deposition method with an anodized porous alumina mask to realize a unit of BiFe_0.9Co_0.1O₃ with single ferroelectric domain. BiFe_0.9Co_0.1O₃/SrRuO₃ nanodots with a diameter of ~60 nm which is as small as a typical scale of ferroelectric domain in BiFe_0.9Co_0.1O₃ films were successfully obtained.