We measured the upper critical field H-c2 and the critical current density J(c) on neutron-irradiated MgB2 samples and studied the effects of damaging on pinning mechanisms. We observed a strong enhancement of the upper critical field and great improvement of the critical current magnetic field dependence in an intermediate range of fluence. We demonstrated that the critical current increase is not only due to the H-c2 improvement but the irradiation substantially changes the pinning force improving the critical current density at high magnetic field. (C) 2007 Elsevier B.V. All rights reserved.