Using atomic force microscope (AFM), we have investigated the correlation between the characteristics of grooved SrTiO 3 (STO) bicrystal line and the grain-boundary (GB) microstructure of the YBa 2Cu 3O y (YBCO) film. When the underlying groove becomes deeper and steeper, the density of growth spirals along the boundary line increases and the meandering configuration of GB gradually disappears. From the measured signals of the dc-SQUIDs patterned on the films, we also conclude that the homogeneity of the GB is improved.