On the trunk, it appears that font anti-aliasing is turned off on rotated text, as in this example: n [26]: import datetime In [27]: dt = datetime.date.today() In [28]: dates = [dt-datetime.timedelta(days=i) for i in range(10)] In [29]: plot(dates, range(10)) Out[29]: [<matplotlib.lines.Line2D object at 0x98f96ac>] # after rotation the fonts are pixelated In [34]: gcf().autofmt_xdate () In [35]: draw()