You can use DateFormatter
:
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot(your_dates, your_data)
# format your data to desired format. Here I chose YYYY-MM-DD but you can set it to whatever you want.
import matplotlib.dates as mdates
ax.xaxis.set_major_formatter(mdates.DateFormatter('%Y-%m-%d'))
# rotate and align the tick labels so they look better
fig.autofmt_xdate()