BiMnO₃ has been a promising candidate as a magnetoelectric multiferroic while there have been many
controversial reports on its ferroelectricity. The detailed analysis of its film growth, especially the growth of thin film having monoclinic symmetry has not been reported. We studied the effect of miscut angle, the substrate surface, and film thickness on the symmetry of BiMnO₃ thin film. A flat SrTiO₃ (110) substrate resulted in a thin film with three domains of BiMnO₃ and 1 degree miscut in the SrTiO₃ (110) substrate resulted in dominant domain preference in the BiMnO₃ thin film. The larger miscut resulted in a nearly perfect detwinned BiMnO₃ film with a monoclinic phase. This strong power of domain selection due to the step edge of the substrate was efficient even for the thicker film which showed a rather relaxed growth behavior along the SrTiO₃ [1-10] direction.