Proton beams with energies of 10 and 200 MeV were irradiated onto InAs quantum dot lasers with a wavelength of 1.3 mu m. The increase in threshold current by proton irradiation was small compared with those of the previously reported other quantum dot lasers with larger active region and 1.3-mu m InGaAsP quantum well lasers. These results were discussed by taking account of non-ionizing energy loss and effective volume of active region. (c) 2008 Elsevier B. V. All rights reserved.