A detailed study is presented on the influence of Mn-doping on densities of screw (c-type) and edge (a-type) threading dislocations (TDs) in Ga1-xMnxN grown by metal organic chemical vapor deposition (MOCVD) by using high-resolution X-ray diffraction (XRD). Three regions were present in Mn source rate dependence plots of density of c-TDs, and the mean twist angle corresponding to the density of a-TDs. In each region, Mn-doping exhibits different effects on the densities of a- and c-TDs, which is attributed to different dependences of the two types of TD on stresses. The results obtained from X-ray diffraction are consistent with those of atomic force microscope (AFM) measurements. It is further suggested that similar phenomena would occur when doping other elements into GaN grown by MOCVD. (C) 2008 Elsevier B.V. All rights reserved.