Brane interaction in the brane world in superstring theory provides a natural framework for the inflationary scenario. Brane inflation, where branes move towards each other, ends when branes collide and heat the universe. Towards the end of the inflationary epoch, cosmic strings (but not domain walls or monopoles) are copiously produced during brane collision. Using the COBE data, the cosmic string tension is estimated to have a value that is consistent with all present known bounds, but should be readily testable in the near future via the cosmic microwave background radiation measurements and gravitational wave detections.