  The cosmological constant on a D-brane is analyzed. This D-brane is in the
background produced by the p-brane solutions. The energy-momentum tensor in
this model has been found and the form of the cosmological constant has been
derived. This energy-momentum tensor is interpreted as an energy-momentum
tensor for a perfect fluid on the D-brane. The energy density and the pressure
for this fluid have been derived. As it turned out the pressure is negative but
the speed of sound is real.
