The Y1-xYbx/2Gdx/2Ba2Cu3O7-y superconducting samples for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by using the solid-state reaction technique. Resistivity measurements of the samples were performed in QD-PPMS system under different magnetic fields up to 5 T in zero fields cooling regime. Using the resistivity data, the upper critical magnetic field H-c2(0) at T = 0 K for 50% of R-n was calculated by the extrapolation H-c2(T) to the temperature T = 0 K. The coherence length in T = 0 K were calculated from H-c2(0) and the effects of x in the composition on both the coherence length and the upper critical magnetic field were examined. The results showed that H-c2(0) Varied from 84.05 to 122.26 T with the content x. The upper critical magnetic field in the temperature T = 0 K slightly decreased with increasing the content x. Using the content x, the upper critical magnetic field can be controlled and this can be used in the superconductivity applications. (C) 2007 Elsevier B.V. All rights reserved.