By coupling a matrix-assisted laser desorption source to an electric beam deflection setup, we have measured the permanent electric dipole moment of the isolated p-amino benzoic acid (PABA) molecule in the ground state along its principal axis. This is the first measurement of the electric dipole of an isolated push-pull molecule. The experimental value is compared to different calculations, and the accuracy of Hartree-Fock and density functional approaches to predict the electronic properties of pi-conjugated systems is discussed.