  We study a cosmological model with a fermionic field which can be interpreted
as a source of dark energy in the universe. Two different approaches were
considered, the first one with a massless fermionic field represented by a
standard wave-function and the second one where a massive field is a Grassmann
variable. {The first case naturally reduces to a XCDM model with a constant
equation of state parameter, while the last case reproduces a $w(z)$CDM model
for a massive field}, and in the massless limit, the intrinsic grassmannian
property of the field leads always to a vacuum equation of state parameter,
irrespective the specific form of the potential. Both cases leads to a dark
energy contribution of the fermionic sector. The models are totally compatible
with recent cosmological data from Supernovae, BAO and Hubble parameter
measurements. A brief study of linear evolution of density perturbations shows
that some of the small scale problems related to standard model can be at least
alleviated.
