You can use BDay() to get the business days in range. For example - 
from pandas.tseries.offsets import *
In [185]: s
Out[185]: 
2011-01-01   -0.011629
2011-01-02   -0.089666
2011-01-03   -1.314430
2011-01-04   -1.867307
2011-01-05    0.779609
2011-01-06    0.588950
2011-01-07   -2.505803
2011-01-08    0.800262
2011-01-09    0.376406
2011-01-10   -0.469988
Freq: D
In [186]: s.asfreq(BDay())
Out[186]: 
2011-01-03   -1.314430
2011-01-04   -1.867307
2011-01-05    0.779609
2011-01-06    0.588950
2011-01-07   -2.505803
2011-01-10   -0.469988
Freq: B