Density functional theory and a virial approach are used to calculate the surface tension and bending rigidity of the interface between demixed fluid phases for a colloid-polymer mixture. The calculated surface tension compares well with results from computers simulations and experiments. The bending rigidity obtained from both theoretical approaches is negative (approximate to -0.1k(B)T), its magnitude increases away from the critical point and it is in reasonable agreement with computer simulations. (C) 2007 Elsevier Inc. All rights reserved.