We have performed large-scale configuration interaction calculations for the electronic states of KRb dissociating into 4s + 5s, 4s + 5p, 4p + 5s, 4s + 4d, 3s + 6s, 5s + 5s, 3d + 5s, 5s + 6p and 5s + 5d using the averaged relativistic effective core potentials. The core-valence correlation effect has been included through the use of the core-polarization potential. The core-core repulsion has been explicitly included by using small-core potential. Comparison with previous calculations without this term shows significant changes of the spectroscopic constants. The spin-orbit effect has been calculated by employing relativistic effective core potentials with spin-orbit operators. The most important changes caused by the spin-orbit interaction is the transformation of the 1 (3)Pi and 2(1)Sigma(+) states into five states characterized by the Ohm quantum number. The 1 (1)Pi state appears to be significantly perturbed by the 2(3)Sigma(+) state through the spin-orbit coupling. The electric dipole moments and transition dipole moments for the excited states are also computed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.