import matplotlib.pyplot as plt from mpl_toolkits.axes_grid.anchored_artists import AnchoredText fig=plt.figure(1, figsize=(3,3)) ax = plt.subplot(111) at = AnchoredText("Figure 1a", prop=dict(size=15), frameon=True, loc=2, ) at.patch.set_boxstyle("round,pad=0.,rounding_size=0.2") ax.add_artist(at) plt.show()