In [1]: import numpy as np In [2]: import pandas as pd In [5]: p1 = pd.Panel([[[0,1],[2,np.nan]], [[10,11],[12,np.nan]]], items=['a','b'], minor_axis=['x','y']) In [7]: p1['a'] Out[7]: x y 0 0.0 1.0 1 2.0 NaN In [8]: p1['b'] Out[8]: x y 0 10.0 11.0 1 12.0 NaN In [9]: p1.fillna(method='ffill', inplace=True) Out[9]: <class 'pandas.core.panel.Panel'> Dimensions: 2 (items) x 2 (major_axis) x 2 (minor_axis) Items axis: a to b Major_axis axis: 0 to 1 Minor_axis axis: x to y In [10]: p1['a'] Out[10]: x y 0 0.0 1.0 1 2.0 NaN In [11]: p1['b'] Out[11]: x y 0 10.0 11.0 1 12.0 NaN In [12]: p2 = p1.fillna(method='ffill', inplace=True) In [13]: p2['a'] Out[13]: x y 0 0.0 1.0 1 2.0 1.0 In [14]: p2['b'] Out[14]: x y 0 10.0 11.0 1 12.0 11.0 In [15]: pd.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.4.4.final.0 python-bits: 64 OS: Windows OS-release: 10 machine: AMD64 processor: Intel64 Family 6 Model 62 Stepping 4, GenuineIntel byteorder: little LC_ALL: None LANG: None pandas: 0.18.0 nose: 1.3.7 pip: 8.1.0 setuptools: 20.2.2 Cython: None numpy: 1.10.4 scipy: 0.17.0 statsmodels: 0.6.1 xarray: 0.7.1 IPython: 4.1.2 sphinx: None patsy: 0.4.1 dateutil: 2.5.0 pytz: 2016.1 blosc: None bottleneck: None tables: 3.2.2 numexpr: 2.5 matplotlib: 1.5.1 openpyxl: 2.3.3 xlrd: None xlwt: None xlsxwriter: None lxml: None bs4: 4.4.1 html5lib: 1.0b8 httplib2: None apiclient: None sqlalchemy: 1.0.12 pymysql: None psycopg2: 2.6.1 (dt dec pq3 ext lo64) jinja2: 2.8 boto: None