  The element abundance distributions in the ejecta of Type Ia supernova (SN)
is studied by modelling a time series of optical spectra of SN 2003du until ~1
year after the explosion. Since SN 2003du is a very normal Type Ia SN both
photometrically and spectroscopically, the abundance distribution derived for
it can be considered as representative of normal Type Ia SNe. We find that the
innermost layers are dominated by stable Fe-group elements, with a total mass
of ~ 0.2 Msun, which are synthesized through electron capture. Above the core
of stable elements there are thick 56Ni-rich layers. The total mass of 56Ni is
0.65 Msun. The Si- and S-rich layers are located above the 56Ni-rich layers.
The dominant element in the outermost layers (M_r > 1.1 Msun, v > 13000 km/s)
is O, with a small amount of Si. Little unburned C remains, with an upper limit
of 0.016 Msun. The element distributions in the ejecta are moderately mixed,
but not fully mixed as seen in three-dimensional deflagration models.
